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<header> 91 <div class="header-container"> 92 <h1>Node.js v14.21.2 documentation</h1> 93 <button class="theme-toggle-btn" id="theme-toggle-btn" title="Toggle dark mode/light mode" aria-label="Toggle dark mode/light mode" hidden> 94 <svg xmlns="http://www.w3.org/2000/svg" class="icon dark-icon" height="24" width="24"> 95 <path fill="none" d="M0 0h24v24H0z" /> 96 <path d="M11.1 12.08c-2.33-4.51-.5-8.48.53-10.07C6.27 2.2 1.98 6.59 1.98 12c0 .14.02.28.02.42.62-.27 1.29-.42 2-.42 1.66 0 3.18.83 4.1 2.15A4.01 4.01 0 0111 18c0 1.52-.87 2.83-2.12 3.51.98.32 2.03.5 3.11.5 3.5 0 6.58-1.8 8.37-4.52-2.36.23-6.98-.97-9.26-5.41z"/> 97 <path d="M7 16h-.18C6.4 14.84 5.3 14 4 14c-1.66 0-3 1.34-3 3s1.34 3 3 3h3c1.1 0 2-.9 2-2s-.9-2-2-2z"/> 98 </svg> 99 <svg xmlns="http://www.w3.org/2000/svg" class="icon light-icon" height="24" width="24"> 100 <path d="M0 0h24v24H0z" fill="none" /> 101 <path d="M6.76 4.84l-1.8-1.79-1.41 1.41 1.79 1.79 1.42-1.41zM4 10.5H1v2h3v-2zm9-9.95h-2V3.5h2V.55zm7.45 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135<li><a href="https://nodejs.org/docs/latest-v0.12.x/api/assert.html">0.12.x</a></li> 136<li><a href="https://nodejs.org/docs/latest-v0.10.x/api/assert.html">0.10.x</a></li></ol> 137 </li> 138 139 <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/master/doc/api/assert.md">Edit on GitHub</a></li> 140 </ul> 141 </div> 142 <hr> 143 </header> 144 145 <details id="toc" open><summary>Table of contents</summary><ul> 146<li><span class="stability_2"><a href="#assert_assert">Assert</a></span> 147<ul> 148<li><a href="#assert_strict_assertion_mode">Strict assertion mode</a></li> 149<li><a href="#assert_legacy_assertion_mode">Legacy assertion mode</a></li> 150<li><a href="#assert_class_assert_assertionerror">Class: assert.AssertionError</a> 151<ul> 152<li><a href="#assert_new_assert_assertionerror_options"><code>new assert.AssertionError(options)</code></a></li> 153</ul> 154</li> 155<li><span class="stability_1"><a href="#assert_class_assert_calltracker">Class: <code>assert.CallTracker</code></a></span> 156<ul> 157<li><a href="#assert_new_assert_calltracker"><code>new assert.CallTracker()</code></a></li> 158<li><a href="#assert_tracker_calls_fn_exact"><code>tracker.calls([fn][, exact])</code></a></li> 159<li><a href="#assert_tracker_report"><code>tracker.report()</code></a></li> 160<li><a href="#assert_tracker_verify"><code>tracker.verify()</code></a></li> 161</ul> 162</li> 163<li><a href="#assert_assert_value_message"><code>assert(value[, message])</code></a></li> 164<li><a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual(actual, expected[, message])</code></a> 165<ul> 166<li><a href="#assert_comparison_details">Comparison details</a></li> 167</ul> 168</li> 169<li><a href="#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual(actual, expected[, message])</code></a> 170<ul> 171<li><a href="#assert_comparison_details_1">Comparison details</a></li> 172</ul> 173</li> 174<li><span class="stability_1"><a href="#assert_assert_doesnotmatch_string_regexp_message"><code>assert.doesNotMatch(string, regexp[, message])</code></a></span></li> 175<li><a href="#assert_assert_doesnotreject_asyncfn_error_message"><code>assert.doesNotReject(asyncFn[, error][, message])</code></a></li> 176<li><a href="#assert_assert_doesnotthrow_fn_error_message"><code>assert.doesNotThrow(fn[, error][, message])</code></a></li> 177<li><a href="#assert_assert_equal_actual_expected_message"><code>assert.equal(actual, expected[, message])</code></a></li> 178<li><a href="#assert_assert_fail_message"><code>assert.fail([message])</code></a></li> 179<li><span class="stability_0"><a href="#assert_assert_fail_actual_expected_message_operator_stackstartfn"><code>assert.fail(actual, expected[, message[, operator[, stackStartFn]]])</code></a></span></li> 180<li><a href="#assert_assert_iferror_value"><code>assert.ifError(value)</code></a></li> 181<li><span class="stability_1"><a href="#assert_assert_match_string_regexp_message"><code>assert.match(string, regexp[, message])</code></a></span></li> 182<li><a href="#assert_assert_notdeepequal_actual_expected_message"><code>assert.notDeepEqual(actual, expected[, message])</code></a></li> 183<li><a href="#assert_assert_notdeepstrictequal_actual_expected_message"><code>assert.notDeepStrictEqual(actual, expected[, message])</code></a></li> 184<li><a href="#assert_assert_notequal_actual_expected_message"><code>assert.notEqual(actual, expected[, message])</code></a></li> 185<li><a href="#assert_assert_notstrictequal_actual_expected_message"><code>assert.notStrictEqual(actual, expected[, message])</code></a></li> 186<li><a href="#assert_assert_ok_value_message"><code>assert.ok(value[, message])</code></a></li> 187<li><a href="#assert_assert_rejects_asyncfn_error_message"><code>assert.rejects(asyncFn[, error][, message])</code></a></li> 188<li><a href="#assert_assert_strictequal_actual_expected_message"><code>assert.strictEqual(actual, expected[, message])</code></a></li> 189<li><a href="#assert_assert_throws_fn_error_message"><code>assert.throws(fn[, error][, message])</code></a></li> 190</ul> 191</li> 192</ul></details> 193 194 <div id="apicontent"> 195 <h2>Assert<span><a class="mark" href="#assert_assert" id="assert_assert">#</a></span></h2> 196 197<p></p><div class="api_stability api_stability_2"><a href="documentation.html#documentation_stability_index">Stability: 2</a> - Stable</div><p></p> 198<p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v14.21.2/lib/assert.js">lib/assert.js</a></p> 199<p>The <code>assert</code> module provides a set of assertion functions for verifying 200invariants.</p> 201<section><h3>Strict assertion mode<span><a class="mark" href="#assert_strict_assertion_mode" id="assert_strict_assertion_mode">#</a></span></h3> 202<div class="api_metadata"> 203<details class="changelog"><summary>History</summary> 204<table> 205<tbody><tr><th>Version</th><th>Changes</th></tr> 206<tr><td>v13.9.0, v12.16.2</td> 207<td><p>Changed "strict mode" to "strict assertion mode" and "legacy mode" to "legacy assertion mode" to avoid confusion with the more usual meaning of "strict mode".</p></td></tr> 208<tr><td>v9.9.0</td> 209<td><p>Added error diffs to the strict assertion mode.</p></td></tr> 210<tr><td>v9.9.0</td> 211<td><p>Added strict assertion mode to the assert module.</p></td></tr> 212<tr><td>v9.9.0</td> 213<td><p><span>Added in: v9.9.0</span></p></td></tr> 214</tbody></table> 215</details> 216</div> 217<p>In strict assertion mode, non-strict methods behave like their corresponding 218strict methods. For example, <a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual()</code></a> will behave like 219<a href="#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual()</code></a>.</p> 220<p>In strict assertion mode, error messages for objects display a diff. In legacy 221assertion mode, error messages for objects display the objects, often truncated.</p> 222<p>To use strict assertion mode:</p> 223<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>).<span class="hljs-property">strict</span>;</code></pre> 224<p>Example error diff:</p> 225<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>).<span class="hljs-property">strict</span>; 226 227assert.<span class="hljs-title function_">deepEqual</span>([[[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>]], <span class="hljs-number">4</span>, <span class="hljs-number">5</span>], [[[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-string">'3'</span>]], <span class="hljs-number">4</span>, <span class="hljs-number">5</span>]); 228<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span> 229<span class="hljs-comment">// + actual - expected ... Lines skipped</span> 230<span class="hljs-comment">//</span> 231<span class="hljs-comment">// [</span> 232<span class="hljs-comment">// [</span> 233<span class="hljs-comment">// ...</span> 234<span class="hljs-comment">// 2,</span> 235<span class="hljs-comment">// + 3</span> 236<span class="hljs-comment">// - '3'</span> 237<span class="hljs-comment">// ],</span> 238<span class="hljs-comment">// ...</span> 239<span class="hljs-comment">// 5</span> 240<span class="hljs-comment">// ]</span></code></pre> 241<p>To deactivate the colors, use the <code>NO_COLOR</code> or <code>NODE_DISABLE_COLORS</code> 242environment variables. This will also deactivate the colors in the REPL. For 243more on color support in terminal environments, read the tty 244<a href="tty.html#tty_writestream_getcolordepth_env">getColorDepth()</a> documentation.</p> 245</section><section><h3>Legacy assertion mode<span><a class="mark" href="#assert_legacy_assertion_mode" id="assert_legacy_assertion_mode">#</a></span></h3> 246<p>Legacy assertion mode uses the <a href="https://tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</a> in:</p> 247<ul> 248<li><a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual()</code></a></li> 249<li><a href="#assert_assert_equal_actual_expected_message"><code>assert.equal()</code></a></li> 250<li><a href="#assert_assert_notdeepequal_actual_expected_message"><code>assert.notDeepEqual()</code></a></li> 251<li><a href="#assert_assert_notequal_actual_expected_message"><code>assert.notEqual()</code></a></li> 252</ul> 253<p>To use legacy assertion mode:</p> 254<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>);</code></pre> 255<p>Whenever possible, use the <a href="#assert_strict_assertion_mode">strict assertion mode</a> instead. Otherwise, the 256<a href="https://tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</a> may cause surprising results. This is 257especially true for <a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual()</code></a>, where the comparison rules are 258lax:</p> 259<pre><code class="language-js"><span class="hljs-comment">// WARNING: This does not throw an AssertionError!</span> 260assert.<span class="hljs-title function_">deepEqual</span>(<span class="hljs-regexp">/a/gi</span>, <span class="hljs-keyword">new</span> <span class="hljs-title class_">Date</span>());</code></pre> 261</section><section><h3>Class: assert.AssertionError<a class="srclink" href="https://github.com/nodejs/node/blob/92caea621d0fea47ef5af0b3dda427ac2fe2df3f/lib/assert.js#L172">[src]</a><span><a class="mark" href="#assert_class_assert_assertionerror" id="assert_class_assert_assertionerror">#</a></span></h3> 262<ul> 263<li>Extends: <a href="errors.html#errors_class_error" class="type"><errors.Error></a></li> 264</ul> 265<p>Indicates the failure of an assertion. All errors thrown by the <code>assert</code> module 266will be instances of the <code>AssertionError</code> class.</p> 267<h4><code>new assert.AssertionError(options)</code><span><a class="mark" href="#assert_new_assert_assertionerror_options" id="assert_new_assert_assertionerror_options">#</a></span></h4> 268<div class="api_metadata"> 269<span>Added in: v0.1.21</span> 270</div> 271<ul> 272<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 273<ul> 274<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> If provided, the error message is set to this value.</li> 275<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> The <code>actual</code> property on the error instance.</li> 276<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> The <code>expected</code> property on the error instance.</li> 277<li><code>operator</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The <code>operator</code> property on the error instance.</li> 278<li><code>stackStartFn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> If provided, the generated stack trace omits 279frames before this function.</li> 280</ul> 281</li> 282</ul> 283<p>A subclass of <code>Error</code> that indicates the failure of an assertion.</p> 284<p>All instances contain the built-in <code>Error</code> properties (<code>message</code> and <code>name</code>) 285and:</p> 286<ul> 287<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> Set to the <code>actual</code> argument for methods such as 288<a href="#assert_assert_strictequal_actual_expected_message"><code>assert.strictEqual()</code></a>.</li> 289<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> Set to the <code>expected</code> value for methods such as 290<a href="#assert_assert_strictequal_actual_expected_message"><code>assert.strictEqual()</code></a>.</li> 291<li><code>generatedMessage</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> Indicates if the message was auto-generated 292(<code>true</code>) or not.</li> 293<li><code>code</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Value is always <code>ERR_ASSERTION</code> to show that the error is an 294assertion error.</li> 295<li><code>operator</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Set to the passed in operator value.</li> 296</ul> 297<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>); 298 299<span class="hljs-comment">// Generate an AssertionError to compare the error message later:</span> 300<span class="hljs-keyword">const</span> { message } = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">AssertionError</span>({ 301 <span class="hljs-attr">actual</span>: <span class="hljs-number">1</span>, 302 <span class="hljs-attr">expected</span>: <span class="hljs-number">2</span>, 303 <span class="hljs-attr">operator</span>: <span class="hljs-string">'strictEqual'</span> 304}); 305 306<span class="hljs-comment">// Verify error output:</span> 307<span class="hljs-keyword">try</span> { 308 assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>); 309} <span class="hljs-keyword">catch</span> (err) { 310 <span class="hljs-title function_">assert</span>(err <span class="hljs-keyword">instanceof</span> assert.<span class="hljs-property">AssertionError</span>); 311 assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">message</span>, message); 312 assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">name</span>, <span class="hljs-string">'AssertionError'</span>); 313 assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">actual</span>, <span class="hljs-number">1</span>); 314 assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">expected</span>, <span class="hljs-number">2</span>); 315 assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">code</span>, <span class="hljs-string">'ERR_ASSERTION'</span>); 316 assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">operator</span>, <span class="hljs-string">'strictEqual'</span>); 317 assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">generatedMessage</span>, <span class="hljs-literal">true</span>); 318}</code></pre> 319</section><section><h3>Class: <code>assert.CallTracker</code><span><a class="mark" href="#assert_class_assert_calltracker" id="assert_class_assert_calltracker">#</a></span></h3> 320<div class="api_metadata"> 321<span>Added in: v14.2.0</span> 322</div> 323<p></p><div class="api_stability api_stability_1"><a href="documentation.html#documentation_stability_index">Stability: 1</a> - Experimental</div><p></p> 324<p>This feature is currently experimental and behavior might still change.</p> 325<h4><code>new assert.CallTracker()</code><span><a class="mark" href="#assert_new_assert_calltracker" id="assert_new_assert_calltracker">#</a></span></h4> 326<div class="api_metadata"> 327<span>Added in: v14.2.0</span> 328</div> 329<p>Creates a new <a href="#assert_class_assert_calltracker"><code>CallTracker</code></a> object which can be used to track if functions 330were called a specific number of times. The <code>tracker.verify()</code> must be called 331for the verification to take place. The usual pattern would be to call it in a 332<a href="process.html#process_event_exit"><code>process.on('exit')</code></a> handler.</p> 333<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>); 334 335<span class="hljs-keyword">const</span> tracker = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">CallTracker</span>(); 336 337<span class="hljs-keyword">function</span> <span class="hljs-title function_">func</span>(<span class="hljs-params"></span>) {} 338 339<span class="hljs-comment">// callsfunc() must be called exactly 1 time before tracker.verify().</span> 340<span class="hljs-keyword">const</span> callsfunc = tracker.<span class="hljs-title function_">calls</span>(func, <span class="hljs-number">1</span>); 341 342<span class="hljs-title function_">callsfunc</span>(); 343 344<span class="hljs-comment">// Calls tracker.verify() and verifies if all tracker.calls() functions have</span> 345<span class="hljs-comment">// been called exact times.</span> 346process.<span class="hljs-title function_">on</span>(<span class="hljs-string">'exit'</span>, <span class="hljs-function">() =></span> { 347 tracker.<span class="hljs-title function_">verify</span>(); 348});</code></pre> 349<h4><code>tracker.calls([fn][, exact])</code><span><a class="mark" href="#assert_tracker_calls_fn_exact" id="assert_tracker_calls_fn_exact">#</a></span></h4> 350<div class="api_metadata"> 351<span>Added in: v14.2.0</span> 352</div> 353<ul> 354<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> <strong>Default</strong> A no-op function.</li> 355<li><code>exact</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> <strong>Default</strong> <code>1</code>.</li> 356<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> that wraps <code>fn</code>.</li> 357</ul> 358<p>The wrapper function is expected to be called exactly <code>exact</code> times. If the 359function has not been called exactly <code>exact</code> times when 360<a href="#assert_tracker_verify"><code>tracker.verify()</code></a> is called, then <a href="#assert_tracker_verify"><code>tracker.verify()</code></a> will throw an 361error.</p> 362<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>); 363 364<span class="hljs-comment">// Creates call tracker.</span> 365<span class="hljs-keyword">const</span> tracker = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">CallTracker</span>(); 366 367<span class="hljs-keyword">function</span> <span class="hljs-title function_">func</span>(<span class="hljs-params"></span>) {} 368 369<span class="hljs-comment">// Returns a function that wraps func() that must be called exact times</span> 370<span class="hljs-comment">// before tracker.verify().</span> 371<span class="hljs-keyword">const</span> callsfunc = tracker.<span class="hljs-title function_">calls</span>(func);</code></pre> 372<h4><code>tracker.report()</code><span><a class="mark" href="#assert_tracker_report" id="assert_tracker_report">#</a></span></h4> 373<div class="api_metadata"> 374<span>Added in: v14.2.0</span> 375</div> 376<ul> 377<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> of objects containing information about the wrapper functions 378returned by <a href="#assert_tracker_calls_fn_exact"><code>tracker.calls()</code></a>.</li> 379<li>Object <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 380<ul> 381<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 382<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The actual number of times the function was called.</li> 383<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The number of times the function was expected to be 384called.</li> 385<li><code>operator</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The name of the function that is wrapped.</li> 386<li><code>stack</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> A stack trace of the function.</li> 387</ul> 388</li> 389</ul> 390<p>The arrays contains information about the expected and actual number of calls of 391the functions that have not been called the expected number of times.</p> 392<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>); 393 394<span class="hljs-comment">// Creates call tracker.</span> 395<span class="hljs-keyword">const</span> tracker = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">CallTracker</span>(); 396 397<span class="hljs-keyword">function</span> <span class="hljs-title function_">func</span>(<span class="hljs-params"></span>) {} 398 399<span class="hljs-keyword">function</span> <span class="hljs-title function_">foo</span>(<span class="hljs-params"></span>) {} 400 401<span class="hljs-comment">// Returns a function that wraps func() that must be called exact times</span> 402<span class="hljs-comment">// before tracker.verify().</span> 403<span class="hljs-keyword">const</span> callsfunc = tracker.<span class="hljs-title function_">calls</span>(func, <span class="hljs-number">2</span>); 404 405<span class="hljs-comment">// Returns an array containing information on callsfunc()</span> 406tracker.<span class="hljs-title function_">report</span>(); 407<span class="hljs-comment">// [</span> 408<span class="hljs-comment">// {</span> 409<span class="hljs-comment">// message: 'Expected the func function to be executed 2 time(s) but was</span> 410<span class="hljs-comment">// executed 0 time(s).',</span> 411<span class="hljs-comment">// actual: 0,</span> 412<span class="hljs-comment">// expected: 2,</span> 413<span class="hljs-comment">// operator: 'func',</span> 414<span class="hljs-comment">// stack: stack trace</span> 415<span class="hljs-comment">// }</span> 416<span class="hljs-comment">// ]</span></code></pre> 417<h4><code>tracker.verify()</code><span><a class="mark" href="#assert_tracker_verify" id="assert_tracker_verify">#</a></span></h4> 418<div class="api_metadata"> 419<span>Added in: v14.2.0</span> 420</div> 421<p>Iterates through the list of functions passed to 422<a href="#assert_tracker_calls_fn_exact"><code>tracker.calls()</code></a> and will throw an error for functions that 423have not been called the expected number of times.</p> 424<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>); 425 426<span class="hljs-comment">// Creates call tracker.</span> 427<span class="hljs-keyword">const</span> tracker = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">CallTracker</span>(); 428 429<span class="hljs-keyword">function</span> <span class="hljs-title function_">func</span>(<span class="hljs-params"></span>) {} 430 431<span class="hljs-comment">// Returns a function that wraps func() that must be called exact times</span> 432<span class="hljs-comment">// before tracker.verify().</span> 433<span class="hljs-keyword">const</span> callsfunc = tracker.<span class="hljs-title function_">calls</span>(func, <span class="hljs-number">2</span>); 434 435<span class="hljs-title function_">callsfunc</span>(); 436 437<span class="hljs-comment">// Will throw an error since callsfunc() was only called once.</span> 438tracker.<span class="hljs-title function_">verify</span>();</code></pre> 439</section><section><h3><code>assert(value[, message])</code><span><a class="mark" href="#assert_assert_value_message" id="assert_assert_value_message">#</a></span></h3> 440<div class="api_metadata"> 441<span>Added in: v0.5.9</span> 442</div> 443<ul> 444<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> The input that is checked for being truthy.</li> 445<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> 446</ul> 447<p>An alias of <a href="#assert_assert_ok_value_message"><code>assert.ok()</code></a>.</p> 448</section><section><h3><code>assert.deepEqual(actual, expected[, message])</code><span><a class="mark" href="#assert_assert_deepequal_actual_expected_message" id="assert_assert_deepequal_actual_expected_message">#</a></span></h3> 449<div class="api_metadata"> 450<details class="changelog"><summary>History</summary> 451<table> 452<tbody><tr><th>Version</th><th>Changes</th></tr> 453<tr><td>v14.18.0</td> 454<td><p>In Legacy assertion mode, changed status from Deprecated to Legacy.</p></td></tr> 455<tr><td>v14.0.0</td> 456<td><p>NaN is now treated as being identical in case both sides are NaN.</p></td></tr> 457<tr><td>v12.0.0</td> 458<td><p>The type tags are now properly compared and there are a couple minor comparison adjustments to make the check less surprising.</p></td></tr> 459<tr><td>v9.0.0</td> 460<td><p>The <code>Error</code> names and messages are now properly compared.</p></td></tr> 461<tr><td>v8.0.0</td> 462<td><p>The <code>Set</code> and <code>Map</code> content is also compared.</p></td></tr> 463<tr><td>v6.4.0, v4.7.1</td> 464<td><p>Typed array slices are handled correctly now.</p></td></tr> 465<tr><td>v6.1.0, v4.5.0</td> 466<td><p>Objects with circular references can be used as inputs now.</p></td></tr> 467<tr><td>v5.10.1, v4.4.3</td> 468<td><p>Handle non-<code>Uint8Array</code> typed arrays correctly.</p></td></tr> 469<tr><td>v0.1.21</td> 470<td><p><span>Added in: v0.1.21</span></p></td></tr> 471</tbody></table> 472</details> 473</div> 474<ul> 475<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 476<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 477<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> 478</ul> 479<p><strong>Strict assertion mode</strong></p> 480<p>An alias of <a href="#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual()</code></a>.</p> 481<p><strong>Legacy assertion mode</strong></p> 482<p></p><div class="api_stability api_stability_3"><a href="documentation.html#documentation_stability_index">Stability: 3</a> - Legacy: Use <a href="#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual()</code></a> instead.</div><p></p> 483<p>Tests for deep equality between the <code>actual</code> and <code>expected</code> parameters. Consider 484using <a href="#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual()</code></a> instead. <a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual()</code></a> can have 485surprising results.</p> 486<p><em>Deep equality</em> means that the enumerable "own" properties of child objects 487are also recursively evaluated by the following rules.</p> 488<h4>Comparison details<span><a class="mark" href="#assert_comparison_details" id="assert_comparison_details">#</a></span></h4> 489<ul> 490<li>Primitive values are compared with the <a href="https://tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</a> 491( <code>==</code> ) with the exception of <code>NaN</code>. It is treated as being identical in case 492both sides are <code>NaN</code>.</li> 493<li><a href="https://tc39.github.io/ecma262/#sec-object.prototype.tostring">Type tags</a> of objects should be the same.</li> 494<li>Only <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties">enumerable "own" properties</a> are considered.</li> 495<li><a href="errors.html#errors_class_error"><code>Error</code></a> names and messages are always compared, even if these are not 496enumerable properties.</li> 497<li><a href="https://developer.mozilla.org/en-US/docs/Glossary/Primitive#Primitive_wrapper_objects_in_JavaScript">Object wrappers</a> are compared both as objects and unwrapped values.</li> 498<li><code>Object</code> properties are compared unordered.</li> 499<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map"><code>Map</code></a> keys and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set"><code>Set</code></a> items are compared unordered.</li> 500<li>Recursion stops when both sides differ or both sides encounter a circular 501reference.</li> 502<li>Implementation does not test the <a href="https://tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots"><code>[[Prototype]]</code></a> of 503objects.</li> 504<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol"><code>Symbol</code></a> properties are not compared.</li> 505<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a> and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> comparison does not rely on their values.</li> 506</ul> 507<p>The following example does not throw an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> because the 508primitives are considered equal by the <a href="https://tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</a> 509( <code>==</code> ).</p> 510<pre><code class="language-js"><span class="hljs-comment">// WARNING: This does not throw an AssertionError!</span> 511assert.<span class="hljs-title function_">deepEqual</span>(<span class="hljs-string">'+00000000'</span>, <span class="hljs-literal">false</span>);</code></pre> 512<p>"Deep" equality means that the enumerable "own" properties of child objects 513are evaluated also:</p> 514<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>); 515 516<span class="hljs-keyword">const</span> obj1 = { 517 <span class="hljs-attr">a</span>: { 518 <span class="hljs-attr">b</span>: <span class="hljs-number">1</span> 519 } 520}; 521<span class="hljs-keyword">const</span> obj2 = { 522 <span class="hljs-attr">a</span>: { 523 <span class="hljs-attr">b</span>: <span class="hljs-number">2</span> 524 } 525}; 526<span class="hljs-keyword">const</span> obj3 = { 527 <span class="hljs-attr">a</span>: { 528 <span class="hljs-attr">b</span>: <span class="hljs-number">1</span> 529 } 530}; 531<span class="hljs-keyword">const</span> obj4 = <span class="hljs-title class_">Object</span>.<span class="hljs-title function_">create</span>(obj1); 532 533assert.<span class="hljs-title function_">deepEqual</span>(obj1, obj1); 534<span class="hljs-comment">// OK</span> 535 536<span class="hljs-comment">// Values of b are different:</span> 537assert.<span class="hljs-title function_">deepEqual</span>(obj1, obj2); 538<span class="hljs-comment">// AssertionError: { a: { b: 1 } } deepEqual { a: { b: 2 } }</span> 539 540assert.<span class="hljs-title function_">deepEqual</span>(obj1, obj3); 541<span class="hljs-comment">// OK</span> 542 543<span class="hljs-comment">// Prototypes are ignored:</span> 544assert.<span class="hljs-title function_">deepEqual</span>(obj1, obj4); 545<span class="hljs-comment">// AssertionError: { a: { b: 1 } } deepEqual {}</span></code></pre> 546<p>If the values are not equal, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code> 547property set equal to the value of the <code>message</code> parameter. If the <code>message</code> 548parameter is undefined, a default error message is assigned. If the <code>message</code> 549parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the 550<a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a>.</p> 551</section><section><h3><code>assert.deepStrictEqual(actual, expected[, message])</code><span><a class="mark" href="#assert_assert_deepstrictequal_actual_expected_message" id="assert_assert_deepstrictequal_actual_expected_message">#</a></span></h3> 552<div class="api_metadata"> 553<details class="changelog"><summary>History</summary> 554<table> 555<tbody><tr><th>Version</th><th>Changes</th></tr> 556<tr><td>v9.0.0</td> 557<td><p>Enumerable symbol properties are now compared.</p></td></tr> 558<tr><td>v9.0.0</td> 559<td><p>The <code>NaN</code> is now compared using the <a href="https://tc39.github.io/ecma262/#sec-samevaluezero">SameValueZero</a> comparison.</p></td></tr> 560<tr><td>v8.5.0</td> 561<td><p>The <code>Error</code> names and messages are now properly compared.</p></td></tr> 562<tr><td>v8.0.0</td> 563<td><p>The <code>Set</code> and <code>Map</code> content is also compared.</p></td></tr> 564<tr><td>v6.1.0</td> 565<td><p>Objects with circular references can be used as inputs now.</p></td></tr> 566<tr><td>v6.4.0, v4.7.1</td> 567<td><p>Typed array slices are handled correctly now.</p></td></tr> 568<tr><td>v5.10.1, v4.4.3</td> 569<td><p>Handle non-<code>Uint8Array</code> typed arrays correctly.</p></td></tr> 570<tr><td>v1.2.0</td> 571<td><p><span>Added in: v1.2.0</span></p></td></tr> 572</tbody></table> 573</details> 574</div> 575<ul> 576<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 577<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 578<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> 579</ul> 580<p>Tests for deep equality between the <code>actual</code> and <code>expected</code> parameters. 581"Deep" equality means that the enumerable "own" properties of child objects 582are recursively evaluated also by the following rules.</p> 583<h4>Comparison details<span><a class="mark" href="#assert_comparison_details_1" id="assert_comparison_details_1">#</a></span></h4> 584<ul> 585<li>Primitive values are compared using the <a href="https://tc39.github.io/ecma262/#sec-samevalue">SameValue Comparison</a>, used by 586<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is"><code>Object.is()</code></a>.</li> 587<li><a href="https://tc39.github.io/ecma262/#sec-object.prototype.tostring">Type tags</a> of objects should be the same.</li> 588<li><a href="https://tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots"><code>[[Prototype]]</code></a> of objects are compared using 589the <a href="https://tc39.github.io/ecma262/#sec-strict-equality-comparison">Strict Equality Comparison</a>.</li> 590<li>Only <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties">enumerable "own" properties</a> are considered.</li> 591<li><a href="errors.html#errors_class_error"><code>Error</code></a> names and messages are always compared, even if these are not 592enumerable properties.</li> 593<li>Enumerable own <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol"><code>Symbol</code></a> properties are compared as well.</li> 594<li><a href="https://developer.mozilla.org/en-US/docs/Glossary/Primitive#Primitive_wrapper_objects_in_JavaScript">Object wrappers</a> are compared both as objects and unwrapped values.</li> 595<li><code>Object</code> properties are compared unordered.</li> 596<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map"><code>Map</code></a> keys and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set"><code>Set</code></a> items are compared unordered.</li> 597<li>Recursion stops when both sides differ or both sides encounter a circular 598reference.</li> 599<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a> and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> comparison does not rely on their values. See 600below for further details.</li> 601</ul> 602<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>).<span class="hljs-property">strict</span>; 603 604<span class="hljs-comment">// This fails because 1 !== '1'.</span> 605assert.<span class="hljs-title function_">deepStrictEqual</span>({ <span class="hljs-attr">a</span>: <span class="hljs-number">1</span> }, { <span class="hljs-attr">a</span>: <span class="hljs-string">'1'</span> }); 606<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span> 607<span class="hljs-comment">// + actual - expected</span> 608<span class="hljs-comment">//</span> 609<span class="hljs-comment">// {</span> 610<span class="hljs-comment">// + a: 1</span> 611<span class="hljs-comment">// - a: '1'</span> 612<span class="hljs-comment">// }</span> 613 614<span class="hljs-comment">// The following objects don't have own properties</span> 615<span class="hljs-keyword">const</span> date = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Date</span>(); 616<span class="hljs-keyword">const</span> object = {}; 617<span class="hljs-keyword">const</span> fakeDate = {}; 618<span class="hljs-title class_">Object</span>.<span class="hljs-title function_">setPrototypeOf</span>(fakeDate, <span class="hljs-title class_">Date</span>.<span class="hljs-property"><span class="hljs-keyword">prototype</span></span>); 619 620<span class="hljs-comment">// Different [[Prototype]]:</span> 621assert.<span class="hljs-title function_">deepStrictEqual</span>(object, fakeDate); 622<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span> 623<span class="hljs-comment">// + actual - expected</span> 624<span class="hljs-comment">//</span> 625<span class="hljs-comment">// + {}</span> 626<span class="hljs-comment">// - Date {}</span> 627 628<span class="hljs-comment">// Different type tags:</span> 629assert.<span class="hljs-title function_">deepStrictEqual</span>(date, fakeDate); 630<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span> 631<span class="hljs-comment">// + actual - expected</span> 632<span class="hljs-comment">//</span> 633<span class="hljs-comment">// + 2018-04-26T00:49:08.604Z</span> 634<span class="hljs-comment">// - Date {}</span> 635 636assert.<span class="hljs-title function_">deepStrictEqual</span>(<span class="hljs-title class_">Na</span>N, <span class="hljs-title class_">Na</span>N); 637<span class="hljs-comment">// OK, because of the SameValue comparison</span> 638 639<span class="hljs-comment">// Different unwrapped numbers:</span> 640assert.<span class="hljs-title function_">deepStrictEqual</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Number</span>(<span class="hljs-number">1</span>), <span class="hljs-keyword">new</span> <span class="hljs-title class_">Number</span>(<span class="hljs-number">2</span>)); 641<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span> 642<span class="hljs-comment">// + actual - expected</span> 643<span class="hljs-comment">//</span> 644<span class="hljs-comment">// + [Number: 1]</span> 645<span class="hljs-comment">// - [Number: 2]</span> 646 647assert.<span class="hljs-title function_">deepStrictEqual</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">String</span>(<span class="hljs-string">'foo'</span>), <span class="hljs-title class_">Object</span>(<span class="hljs-string">'foo'</span>)); 648<span class="hljs-comment">// OK because the object and the string are identical when unwrapped.</span> 649 650assert.<span class="hljs-title function_">deepStrictEqual</span>(-<span class="hljs-number">0</span>, -<span class="hljs-number">0</span>); 651<span class="hljs-comment">// OK</span> 652 653<span class="hljs-comment">// Different zeros using the SameValue Comparison:</span> 654assert.<span class="hljs-title function_">deepStrictEqual</span>(<span class="hljs-number">0</span>, -<span class="hljs-number">0</span>); 655<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span> 656<span class="hljs-comment">// + actual - expected</span> 657<span class="hljs-comment">//</span> 658<span class="hljs-comment">// + 0</span> 659<span class="hljs-comment">// - -0</span> 660 661<span class="hljs-keyword">const</span> symbol1 = <span class="hljs-title class_">Symbol</span>(); 662<span class="hljs-keyword">const</span> symbol2 = <span class="hljs-title class_">Symbol</span>(); 663assert.<span class="hljs-title function_">deepStrictEqual</span>({ [symbol1]: <span class="hljs-number">1</span> }, { [symbol1]: <span class="hljs-number">1</span> }); 664<span class="hljs-comment">// OK, because it is the same symbol on both objects.</span> 665 666assert.<span class="hljs-title function_">deepStrictEqual</span>({ [symbol1]: <span class="hljs-number">1</span> }, { [symbol2]: <span class="hljs-number">1</span> }); 667<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Inputs identical but not reference equal:</span> 668<span class="hljs-comment">//</span> 669<span class="hljs-comment">// {</span> 670<span class="hljs-comment">// [Symbol()]: 1</span> 671<span class="hljs-comment">// }</span> 672 673<span class="hljs-keyword">const</span> weakMap1 = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WeakMap</span>(); 674<span class="hljs-keyword">const</span> weakMap2 = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WeakMap</span>([[{}, {}]]); 675<span class="hljs-keyword">const</span> weakMap3 = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WeakMap</span>(); 676weakMap3.<span class="hljs-property">unequal</span> = <span class="hljs-literal">true</span>; 677 678assert.<span class="hljs-title function_">deepStrictEqual</span>(weakMap1, weakMap2); 679<span class="hljs-comment">// OK, because it is impossible to compare the entries</span> 680 681<span class="hljs-comment">// Fails because weakMap3 has a property that weakMap1 does not contain:</span> 682assert.<span class="hljs-title function_">deepStrictEqual</span>(weakMap1, weakMap3); 683<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span> 684<span class="hljs-comment">// + actual - expected</span> 685<span class="hljs-comment">//</span> 686<span class="hljs-comment">// WeakMap {</span> 687<span class="hljs-comment">// + [items unknown]</span> 688<span class="hljs-comment">// - [items unknown],</span> 689<span class="hljs-comment">// - unequal: true</span> 690<span class="hljs-comment">// }</span></code></pre> 691<p>If the values are not equal, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code> 692property set equal to the value of the <code>message</code> parameter. If the <code>message</code> 693parameter is undefined, a default error message is assigned. If the <code>message</code> 694parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the 695<code>AssertionError</code>.</p> 696</section><section><h3><code>assert.doesNotMatch(string, regexp[, message])</code><span><a class="mark" href="#assert_assert_doesnotmatch_string_regexp_message" id="assert_assert_doesnotmatch_string_regexp_message">#</a></span></h3> 697<div class="api_metadata"> 698<span>Added in: v13.6.0, v12.16.0</span> 699</div> 700<ul> 701<li><code>string</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 702<li><code>regexp</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a></li> 703<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> 704</ul> 705<p></p><div class="api_stability api_stability_1"><a href="documentation.html#documentation_stability_index">Stability: 1</a> - Experimental</div><p></p> 706<p>Expects the <code>string</code> input not to match the regular expression.</p> 707<p>This feature is currently experimental and the name might change or it might be 708completely removed again.</p> 709<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>).<span class="hljs-property">strict</span>; 710 711assert.<span class="hljs-title function_">doesNotMatch</span>(<span class="hljs-string">'I will fail'</span>, <span class="hljs-regexp">/fail/</span>); 712<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: The input was expected to not match the ...</span> 713 714assert.<span class="hljs-title function_">doesNotMatch</span>(<span class="hljs-number">123</span>, <span class="hljs-regexp">/pass/</span>); 715<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: The "string" argument must be of type string.</span> 716 717assert.<span class="hljs-title function_">doesNotMatch</span>(<span class="hljs-string">'I will pass'</span>, <span class="hljs-regexp">/different/</span>); 718<span class="hljs-comment">// OK</span></code></pre> 719<p>If the values do match, or if the <code>string</code> argument is of another type than 720<code>string</code>, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code> property set equal 721to the value of the <code>message</code> parameter. If the <code>message</code> parameter is 722undefined, a default error message is assigned. If the <code>message</code> parameter is an 723instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the 724<a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a>.</p> 725</section><section><h3><code>assert.doesNotReject(asyncFn[, error][, message])</code><span><a class="mark" href="#assert_assert_doesnotreject_asyncfn_error_message" id="assert_assert_doesnotreject_asyncfn_error_message">#</a></span></h3> 726<div class="api_metadata"> 727<span>Added in: v10.0.0</span> 728</div> 729<ul> 730<li><code>asyncFn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a></li> 731<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> 732<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 733</ul> 734<p>Awaits the <code>asyncFn</code> promise or, if <code>asyncFn</code> is a function, immediately 735calls the function and awaits the returned promise to complete. It will then 736check that the promise is not rejected.</p> 737<p>If <code>asyncFn</code> is a function and it throws an error synchronously, 738<code>assert.doesNotReject()</code> will return a rejected <code>Promise</code> with that error. If 739the function does not return a promise, <code>assert.doesNotReject()</code> will return a 740rejected <code>Promise</code> with an <a href="errors.html#errors_err_invalid_return_value"><code>ERR_INVALID_RETURN_VALUE</code></a> error. In both cases 741the error handler is skipped.</p> 742<p>Using <code>assert.doesNotReject()</code> is actually not useful because there is little 743benefit in catching a rejection and then rejecting it again. Instead, consider 744adding a comment next to the specific code path that should not reject and keep 745error messages as expressive as possible.</p> 746<p>If specified, <code>error</code> can be a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes"><code>Class</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a> or a validation 747function. See <a href="#assert_assert_throws_fn_error_message"><code>assert.throws()</code></a> for more details.</p> 748<p>Besides the async nature to await the completion behaves identically to 749<a href="#assert_assert_doesnotthrow_fn_error_message"><code>assert.doesNotThrow()</code></a>.</p> 750<!-- eslint-disable no-restricted-syntax --> 751<pre><code class="language-js">(<span class="hljs-keyword">async</span> () => { 752 <span class="hljs-keyword">await</span> assert.<span class="hljs-title function_">doesNotReject</span>( 753 <span class="hljs-keyword">async</span> () => { 754 <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>); 755 }, 756 <span class="hljs-title class_">SyntaxError</span> 757 ); 758})();</code></pre> 759<!-- eslint-disable no-restricted-syntax --> 760<pre><code class="language-js">assert.<span class="hljs-title function_">doesNotReject</span>(<span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">reject</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>))) 761 .<span class="hljs-title function_">then</span>(<span class="hljs-function">() =></span> { 762 <span class="hljs-comment">// ...</span> 763 });</code></pre> 764</section><section><h3><code>assert.doesNotThrow(fn[, error][, message])</code><span><a class="mark" href="#assert_assert_doesnotthrow_fn_error_message" id="assert_assert_doesnotthrow_fn_error_message">#</a></span></h3> 765<div class="api_metadata"> 766<details class="changelog"><summary>History</summary> 767<table> 768<tbody><tr><th>Version</th><th>Changes</th></tr> 769<tr><td>v5.11.0, v4.4.5</td> 770<td><p>The <code>message</code> parameter is respected now.</p></td></tr> 771<tr><td>v4.2.0</td> 772<td><p>The <code>error</code> parameter can now be an arrow function.</p></td></tr> 773<tr><td>v0.1.21</td> 774<td><p><span>Added in: v0.1.21</span></p></td></tr> 775</tbody></table> 776</details> 777</div> 778<ul> 779<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> 780<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> 781<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 782</ul> 783<p>Asserts that the function <code>fn</code> does not throw an error.</p> 784<p>Using <code>assert.doesNotThrow()</code> is actually not useful because there 785is no benefit in catching an error and then rethrowing it. Instead, consider 786adding a comment next to the specific code path that should not throw and keep 787error messages as expressive as possible.</p> 788<p>When <code>assert.doesNotThrow()</code> is called, it will immediately call the <code>fn</code> 789function.</p> 790<p>If an error is thrown and it is the same type as that specified by the <code>error</code> 791parameter, then an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown. If the error is of a 792different type, or if the <code>error</code> parameter is undefined, the error is 793propagated back to the caller.</p> 794<p>If specified, <code>error</code> can be a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes"><code>Class</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a> or a validation 795function. See <a href="#assert_assert_throws_fn_error_message"><code>assert.throws()</code></a> for more details.</p> 796<p>The following, for instance, will throw the <a href="errors.html#errors_class_typeerror"><code>TypeError</code></a> because there is no 797matching error type in the assertion:</p> 798<!-- eslint-disable no-restricted-syntax --> 799<pre><code class="language-js">assert.<span class="hljs-title function_">doesNotThrow</span>( 800 <span class="hljs-function">() =></span> { 801 <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>); 802 }, 803 <span class="hljs-title class_">SyntaxError</span> 804);</code></pre> 805<p>However, the following will result in an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> with the message 806'Got unwanted exception...':</p> 807<!-- eslint-disable no-restricted-syntax --> 808<pre><code class="language-js">assert.<span class="hljs-title function_">doesNotThrow</span>( 809 <span class="hljs-function">() =></span> { 810 <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>); 811 }, 812 <span class="hljs-title class_">TypeError</span> 813);</code></pre> 814<p>If an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown and a value is provided for the <code>message</code> 815parameter, the value of <code>message</code> will be appended to the <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> 816message:</p> 817<!-- eslint-disable no-restricted-syntax --> 818<pre><code class="language-js">assert.<span class="hljs-title function_">doesNotThrow</span>( 819 <span class="hljs-function">() =></span> { 820 <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>); 821 }, 822 <span class="hljs-regexp">/Wrong value/</span>, 823 <span class="hljs-string">'Whoops'</span> 824); 825<span class="hljs-comment">// Throws: AssertionError: Got unwanted exception: Whoops</span></code></pre> 826</section><section><h3><code>assert.equal(actual, expected[, message])</code><span><a class="mark" href="#assert_assert_equal_actual_expected_message" id="assert_assert_equal_actual_expected_message">#</a></span></h3> 827<div class="api_metadata"> 828<details class="changelog"><summary>History</summary> 829<table> 830<tbody><tr><th>Version</th><th>Changes</th></tr> 831<tr><td>v14.18.0</td> 832<td><p>In Legacy assertion mode, changed status from Deprecated to Legacy.</p></td></tr> 833<tr><td>v14.0.0</td> 834<td><p>NaN is now treated as being identical in case both sides are NaN.</p></td></tr> 835<tr><td>v0.1.21</td> 836<td><p><span>Added in: v0.1.21</span></p></td></tr> 837</tbody></table> 838</details> 839</div> 840<ul> 841<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 842<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 843<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> 844</ul> 845<p><strong>Strict assertion mode</strong></p> 846<p>An alias of <a href="#assert_assert_strictequal_actual_expected_message"><code>assert.strictEqual()</code></a>.</p> 847<p><strong>Legacy assertion mode</strong></p> 848<p></p><div class="api_stability api_stability_3"><a href="documentation.html#documentation_stability_index">Stability: 3</a> - Legacy: Use <a href="#assert_assert_strictequal_actual_expected_message"><code>assert.strictEqual()</code></a> instead.</div><p></p> 849<p>Tests shallow, coercive equality between the <code>actual</code> and <code>expected</code> parameters 850using the <a href="https://tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</a> ( <code>==</code> ). <code>NaN</code> is special handled 851and treated as being identical in case both sides are <code>NaN</code>.</p> 852<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>); 853 854assert.<span class="hljs-title function_">equal</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>); 855<span class="hljs-comment">// OK, 1 == 1</span> 856assert.<span class="hljs-title function_">equal</span>(<span class="hljs-number">1</span>, <span class="hljs-string">'1'</span>); 857<span class="hljs-comment">// OK, 1 == '1'</span> 858assert.<span class="hljs-title function_">equal</span>(<span class="hljs-title class_">Na</span>N, <span class="hljs-title class_">Na</span>N); 859<span class="hljs-comment">// OK</span> 860 861assert.<span class="hljs-title function_">equal</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>); 862<span class="hljs-comment">// AssertionError: 1 == 2</span> 863assert.<span class="hljs-title function_">equal</span>({ <span class="hljs-attr">a</span>: { <span class="hljs-attr">b</span>: <span class="hljs-number">1</span> } }, { <span class="hljs-attr">a</span>: { <span class="hljs-attr">b</span>: <span class="hljs-number">1</span> } }); 864<span class="hljs-comment">// AssertionError: { a: { b: 1 } } == { a: { b: 1 } }</span></code></pre> 865<p>If the values are not equal, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code> 866property set equal to the value of the <code>message</code> parameter. If the <code>message</code> 867parameter is undefined, a default error message is assigned. If the <code>message</code> 868parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the 869<code>AssertionError</code>.</p> 870</section><section><h3><code>assert.fail([message])</code><span><a class="mark" href="#assert_assert_fail_message" id="assert_assert_fail_message">#</a></span></h3> 871<div class="api_metadata"> 872<span>Added in: v0.1.21</span> 873</div> 874<ul> 875<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a> <strong>Default:</strong> <code>'Failed'</code></li> 876</ul> 877<p>Throws an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> with the provided error message or a default 878error message. If the <code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then 879it will be thrown instead of the <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a>.</p> 880<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>).<span class="hljs-property">strict</span>; 881 882assert.<span class="hljs-title function_">fail</span>(); 883<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Failed</span> 884 885assert.<span class="hljs-title function_">fail</span>(<span class="hljs-string">'boom'</span>); 886<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: boom</span> 887 888assert.<span class="hljs-title function_">fail</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'need array'</span>)); 889<span class="hljs-comment">// TypeError: need array</span></code></pre> 890<p>Using <code>assert.fail()</code> with more than two arguments is possible but deprecated. 891See below for further details.</p> 892</section><section><h3><code>assert.fail(actual, expected[, message[, operator[, stackStartFn]]])</code><span><a class="mark" href="#assert_assert_fail_actual_expected_message_operator_stackstartfn" id="assert_assert_fail_actual_expected_message_operator_stackstartfn">#</a></span></h3> 893<div class="api_metadata"> 894<details class="changelog"><summary>History</summary> 895<table> 896<tbody><tr><th>Version</th><th>Changes</th></tr> 897<tr><td>v10.0.0</td> 898<td><p>Calling <code>assert.fail()</code> with more than one argument is deprecated and emits a warning.</p></td></tr> 899<tr><td>v0.1.21</td> 900<td><p><span>Added in: v0.1.21</span></p></td></tr> 901</tbody></table> 902</details> 903</div> 904<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <code>assert.fail([message])</code> or other assert 905functions instead.</div><p></p> 906<ul> 907<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 908<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 909<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> 910<li><code>operator</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> <strong>Default:</strong> <code>'!='</code></li> 911<li><code>stackStartFn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> <strong>Default:</strong> <code>assert.fail</code></li> 912</ul> 913<p>If <code>message</code> is falsy, the error message is set as the values of <code>actual</code> and 914<code>expected</code> separated by the provided <code>operator</code>. If just the two <code>actual</code> and 915<code>expected</code> arguments are provided, <code>operator</code> will default to <code>'!='</code>. If 916<code>message</code> is provided as third argument it will be used as the error message and 917the other arguments will be stored as properties on the thrown object. If 918<code>stackStartFn</code> is provided, all stack frames above that function will be 919removed from stacktrace (see <a href="errors.html#errors_error_capturestacktrace_targetobject_constructoropt"><code>Error.captureStackTrace</code></a>). If no arguments are 920given, the default message <code>Failed</code> will be used.</p> 921<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>).<span class="hljs-property">strict</span>; 922 923assert.<span class="hljs-title function_">fail</span>(<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>); 924<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: 'a' != 'b'</span> 925 926assert.<span class="hljs-title function_">fail</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-literal">undefined</span>, <span class="hljs-string">'>'</span>); 927<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: 1 > 2</span> 928 929assert.<span class="hljs-title function_">fail</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-string">'fail'</span>); 930<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: fail</span> 931 932assert.<span class="hljs-title function_">fail</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-string">'whoops'</span>, <span class="hljs-string">'>'</span>); 933<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: whoops</span> 934 935assert.<span class="hljs-title function_">fail</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'need array'</span>)); 936<span class="hljs-comment">// TypeError: need array</span></code></pre> 937<p>In the last three cases <code>actual</code>, <code>expected</code>, and <code>operator</code> have no 938influence on the error message.</p> 939<p>Example use of <code>stackStartFn</code> for truncating the exception's stacktrace:</p> 940<pre><code class="language-js"><span class="hljs-keyword">function</span> <span class="hljs-title function_">suppressFrame</span>(<span class="hljs-params"></span>) { 941 assert.<span class="hljs-title function_">fail</span>(<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>, <span class="hljs-literal">undefined</span>, <span class="hljs-string">'!=='</span>, suppressFrame); 942} 943<span class="hljs-title function_">suppressFrame</span>(); 944<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: 'a' !== 'b'</span> 945<span class="hljs-comment">// at repl:1:1</span> 946<span class="hljs-comment">// at ContextifyScript.Script.runInThisContext (vm.js:44:33)</span> 947<span class="hljs-comment">// ...</span></code></pre> 948</section><section><h3><code>assert.ifError(value)</code><span><a class="mark" href="#assert_assert_iferror_value" id="assert_assert_iferror_value">#</a></span></h3> 949<div class="api_metadata"> 950<details class="changelog"><summary>History</summary> 951<table> 952<tbody><tr><th>Version</th><th>Changes</th></tr> 953<tr><td>v10.0.0</td> 954<td><p>Instead of throwing the original error it is now wrapped into an [<code>AssertionError</code>][] that contains the full stack trace.</p></td></tr> 955<tr><td>v10.0.0</td> 956<td><p>Value may now only be <code>undefined</code> or <code>null</code>. Before all falsy values were handled the same as <code>null</code> and did not throw.</p></td></tr> 957<tr><td>v0.1.97</td> 958<td><p><span>Added in: v0.1.97</span></p></td></tr> 959</tbody></table> 960</details> 961</div> 962<ul> 963<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 964</ul> 965<p>Throws <code>value</code> if <code>value</code> is not <code>undefined</code> or <code>null</code>. This is useful when 966testing the <code>error</code> argument in callbacks. The stack trace contains all frames 967from the error passed to <code>ifError()</code> including the potential new frames for 968<code>ifError()</code> itself.</p> 969<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>).<span class="hljs-property">strict</span>; 970 971assert.<span class="hljs-title function_">ifError</span>(<span class="hljs-literal">null</span>); 972<span class="hljs-comment">// OK</span> 973assert.<span class="hljs-title function_">ifError</span>(<span class="hljs-number">0</span>); 974<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 0</span> 975assert.<span class="hljs-title function_">ifError</span>(<span class="hljs-string">'error'</span>); 976<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 'error'</span> 977assert.<span class="hljs-title function_">ifError</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>()); 978<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: Error</span> 979 980<span class="hljs-comment">// Create some random error frames.</span> 981<span class="hljs-keyword">let</span> err; 982(<span class="hljs-keyword">function</span> <span class="hljs-title function_">errorFrame</span>(<span class="hljs-params"></span>) { 983 err = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'test error'</span>); 984})(); 985 986(<span class="hljs-keyword">function</span> <span class="hljs-title function_">ifErrorFrame</span>(<span class="hljs-params"></span>) { 987 assert.<span class="hljs-title function_">ifError</span>(err); 988})(); 989<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: test error</span> 990<span class="hljs-comment">// at ifErrorFrame</span> 991<span class="hljs-comment">// at errorFrame</span></code></pre> 992</section><section><h3><code>assert.match(string, regexp[, message])</code><span><a class="mark" href="#assert_assert_match_string_regexp_message" id="assert_assert_match_string_regexp_message">#</a></span></h3> 993<div class="api_metadata"> 994<span>Added in: v13.6.0, v12.16.0</span> 995</div> 996<ul> 997<li><code>string</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 998<li><code>regexp</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a></li> 999<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> 1000</ul> 1001<p></p><div class="api_stability api_stability_1"><a href="documentation.html#documentation_stability_index">Stability: 1</a> - Experimental</div><p></p> 1002<p>Expects the <code>string</code> input to match the regular expression.</p> 1003<p>This feature is currently experimental and the name might change or it might be 1004completely removed again.</p> 1005<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>).<span class="hljs-property">strict</span>; 1006 1007assert.<span class="hljs-title function_">match</span>(<span class="hljs-string">'I will fail'</span>, <span class="hljs-regexp">/pass/</span>); 1008<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: The input did not match the regular ...</span> 1009 1010assert.<span class="hljs-title function_">match</span>(<span class="hljs-number">123</span>, <span class="hljs-regexp">/pass/</span>); 1011<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: The "string" argument must be of type string.</span> 1012 1013assert.<span class="hljs-title function_">match</span>(<span class="hljs-string">'I will pass'</span>, <span class="hljs-regexp">/pass/</span>); 1014<span class="hljs-comment">// OK</span></code></pre> 1015<p>If the values do not match, or if the <code>string</code> argument is of another type than 1016<code>string</code>, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code> property set equal 1017to the value of the <code>message</code> parameter. If the <code>message</code> parameter is 1018undefined, a default error message is assigned. If the <code>message</code> parameter is an 1019instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the 1020<a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a>.</p> 1021</section><section><h3><code>assert.notDeepEqual(actual, expected[, message])</code><span><a class="mark" href="#assert_assert_notdeepequal_actual_expected_message" id="assert_assert_notdeepequal_actual_expected_message">#</a></span></h3> 1022<div class="api_metadata"> 1023<details class="changelog"><summary>History</summary> 1024<table> 1025<tbody><tr><th>Version</th><th>Changes</th></tr> 1026<tr><td>v14.18.0</td> 1027<td><p>In Legacy assertion mode, changed status from Deprecated to Legacy.</p></td></tr> 1028<tr><td>v14.0.0</td> 1029<td><p>NaN is now treated as being identical in case both sides are NaN.</p></td></tr> 1030<tr><td>v9.0.0</td> 1031<td><p>The <code>Error</code> names and messages are now properly compared.</p></td></tr> 1032<tr><td>v8.0.0</td> 1033<td><p>The <code>Set</code> and <code>Map</code> content is also compared.</p></td></tr> 1034<tr><td>v6.4.0, v4.7.1</td> 1035<td><p>Typed array slices are handled correctly now.</p></td></tr> 1036<tr><td>v6.1.0, v4.5.0</td> 1037<td><p>Objects with circular references can be used as inputs now.</p></td></tr> 1038<tr><td>v5.10.1, v4.4.3</td> 1039<td><p>Handle non-<code>Uint8Array</code> typed arrays correctly.</p></td></tr> 1040<tr><td>v0.1.21</td> 1041<td><p><span>Added in: v0.1.21</span></p></td></tr> 1042</tbody></table> 1043</details> 1044</div> 1045<ul> 1046<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 1047<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 1048<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> 1049</ul> 1050<p><strong>Strict assertion mode</strong></p> 1051<p>An alias of <a href="#assert_assert_notdeepstrictequal_actual_expected_message"><code>assert.notDeepStrictEqual()</code></a>.</p> 1052<p><strong>Legacy assertion mode</strong></p> 1053<p></p><div class="api_stability api_stability_3"><a href="documentation.html#documentation_stability_index">Stability: 3</a> - Legacy: Use <a href="#assert_assert_notdeepstrictequal_actual_expected_message"><code>assert.notDeepStrictEqual()</code></a> instead.</div><p></p> 1054<p>Tests for any deep inequality. Opposite of <a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual()</code></a>.</p> 1055<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>); 1056 1057<span class="hljs-keyword">const</span> obj1 = { 1058 <span class="hljs-attr">a</span>: { 1059 <span class="hljs-attr">b</span>: <span class="hljs-number">1</span> 1060 } 1061}; 1062<span class="hljs-keyword">const</span> obj2 = { 1063 <span class="hljs-attr">a</span>: { 1064 <span class="hljs-attr">b</span>: <span class="hljs-number">2</span> 1065 } 1066}; 1067<span class="hljs-keyword">const</span> obj3 = { 1068 <span class="hljs-attr">a</span>: { 1069 <span class="hljs-attr">b</span>: <span class="hljs-number">1</span> 1070 } 1071}; 1072<span class="hljs-keyword">const</span> obj4 = <span class="hljs-title class_">Object</span>.<span class="hljs-title function_">create</span>(obj1); 1073 1074assert.<span class="hljs-title function_">notDeepEqual</span>(obj1, obj1); 1075<span class="hljs-comment">// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }</span> 1076 1077assert.<span class="hljs-title function_">notDeepEqual</span>(obj1, obj2); 1078<span class="hljs-comment">// OK</span> 1079 1080assert.<span class="hljs-title function_">notDeepEqual</span>(obj1, obj3); 1081<span class="hljs-comment">// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }</span> 1082 1083assert.<span class="hljs-title function_">notDeepEqual</span>(obj1, obj4); 1084<span class="hljs-comment">// OK</span></code></pre> 1085<p>If the values are deeply equal, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a 1086<code>message</code> property set equal to the value of the <code>message</code> parameter. If the 1087<code>message</code> parameter is undefined, a default error message is assigned. If the 1088<code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown 1089instead of the <code>AssertionError</code>.</p> 1090</section><section><h3><code>assert.notDeepStrictEqual(actual, expected[, message])</code><span><a class="mark" href="#assert_assert_notdeepstrictequal_actual_expected_message" id="assert_assert_notdeepstrictequal_actual_expected_message">#</a></span></h3> 1091<div class="api_metadata"> 1092<details class="changelog"><summary>History</summary> 1093<table> 1094<tbody><tr><th>Version</th><th>Changes</th></tr> 1095<tr><td>v9.0.0</td> 1096<td><p>The <code>-0</code> and <code>+0</code> are not considered equal anymore.</p></td></tr> 1097<tr><td>v9.0.0</td> 1098<td><p>The <code>NaN</code> is now compared using the <a href="https://tc39.github.io/ecma262/#sec-samevaluezero">SameValueZero</a> comparison.</p></td></tr> 1099<tr><td>v9.0.0</td> 1100<td><p>The <code>Error</code> names and messages are now properly compared.</p></td></tr> 1101<tr><td>v8.0.0</td> 1102<td><p>The <code>Set</code> and <code>Map</code> content is also compared.</p></td></tr> 1103<tr><td>v6.1.0</td> 1104<td><p>Objects with circular references can be used as inputs now.</p></td></tr> 1105<tr><td>v6.4.0, v4.7.1</td> 1106<td><p>Typed array slices are handled correctly now.</p></td></tr> 1107<tr><td>v5.10.1, v4.4.3</td> 1108<td><p>Handle non-<code>Uint8Array</code> typed arrays correctly.</p></td></tr> 1109<tr><td>v1.2.0</td> 1110<td><p><span>Added in: v1.2.0</span></p></td></tr> 1111</tbody></table> 1112</details> 1113</div> 1114<ul> 1115<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 1116<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 1117<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> 1118</ul> 1119<p>Tests for deep strict inequality. Opposite of <a href="#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual()</code></a>.</p> 1120<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>).<span class="hljs-property">strict</span>; 1121 1122assert.<span class="hljs-title function_">notDeepStrictEqual</span>({ <span class="hljs-attr">a</span>: <span class="hljs-number">1</span> }, { <span class="hljs-attr">a</span>: <span class="hljs-string">'1'</span> }); 1123<span class="hljs-comment">// OK</span></code></pre> 1124<p>If the values are deeply and strictly equal, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown 1125with a <code>message</code> property set equal to the value of the <code>message</code> parameter. If 1126the <code>message</code> parameter is undefined, a default error message is assigned. If 1127the <code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown 1128instead of the <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a>.</p> 1129</section><section><h3><code>assert.notEqual(actual, expected[, message])</code><span><a class="mark" href="#assert_assert_notequal_actual_expected_message" id="assert_assert_notequal_actual_expected_message">#</a></span></h3> 1130<div class="api_metadata"> 1131<details class="changelog"><summary>History</summary> 1132<table> 1133<tbody><tr><th>Version</th><th>Changes</th></tr> 1134<tr><td>v14.18.0</td> 1135<td><p>In Legacy assertion mode, changed status from Deprecated to Legacy.</p></td></tr> 1136<tr><td>v14.0.0</td> 1137<td><p>NaN is now treated as being identical in case both sides are NaN.</p></td></tr> 1138<tr><td>v0.1.21</td> 1139<td><p><span>Added in: v0.1.21</span></p></td></tr> 1140</tbody></table> 1141</details> 1142</div> 1143<ul> 1144<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 1145<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 1146<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> 1147</ul> 1148<p><strong>Strict assertion mode</strong></p> 1149<p>An alias of <a href="#assert_assert_notstrictequal_actual_expected_message"><code>assert.notStrictEqual()</code></a>.</p> 1150<p><strong>Legacy assertion mode</strong></p> 1151<p></p><div class="api_stability api_stability_3"><a href="documentation.html#documentation_stability_index">Stability: 3</a> - Legacy: Use <a href="#assert_assert_notstrictequal_actual_expected_message"><code>assert.notStrictEqual()</code></a> instead.</div><p></p> 1152<p>Tests shallow, coercive inequality with the <a href="https://tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</a> 1153(<code>!=</code> ). <code>NaN</code> is special handled and treated as being identical in case both 1154sides are <code>NaN</code>.</p> 1155<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>); 1156 1157assert.<span class="hljs-title function_">notEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>); 1158<span class="hljs-comment">// OK</span> 1159 1160assert.<span class="hljs-title function_">notEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>); 1161<span class="hljs-comment">// AssertionError: 1 != 1</span> 1162 1163assert.<span class="hljs-title function_">notEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-string">'1'</span>); 1164<span class="hljs-comment">// AssertionError: 1 != '1'</span></code></pre> 1165<p>If the values are equal, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code> 1166property set equal to the value of the <code>message</code> parameter. If the <code>message</code> 1167parameter is undefined, a default error message is assigned. If the <code>message</code> 1168parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the 1169<code>AssertionError</code>.</p> 1170</section><section><h3><code>assert.notStrictEqual(actual, expected[, message])</code><span><a class="mark" href="#assert_assert_notstrictequal_actual_expected_message" id="assert_assert_notstrictequal_actual_expected_message">#</a></span></h3> 1171<div class="api_metadata"> 1172<details class="changelog"><summary>History</summary> 1173<table> 1174<tbody><tr><th>Version</th><th>Changes</th></tr> 1175<tr><td>v10.0.0</td> 1176<td><p>Used comparison changed from Strict Equality to <code>Object.is()</code>.</p></td></tr> 1177<tr><td>v0.1.21</td> 1178<td><p><span>Added in: v0.1.21</span></p></td></tr> 1179</tbody></table> 1180</details> 1181</div> 1182<ul> 1183<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 1184<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 1185<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> 1186</ul> 1187<p>Tests strict inequality between the <code>actual</code> and <code>expected</code> parameters as 1188determined by the <a href="https://tc39.github.io/ecma262/#sec-samevalue">SameValue Comparison</a>.</p> 1189<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>).<span class="hljs-property">strict</span>; 1190 1191assert.<span class="hljs-title function_">notStrictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>); 1192<span class="hljs-comment">// OK</span> 1193 1194assert.<span class="hljs-title function_">notStrictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>); 1195<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Expected "actual" to be strictly unequal to:</span> 1196<span class="hljs-comment">//</span> 1197<span class="hljs-comment">// 1</span> 1198 1199assert.<span class="hljs-title function_">notStrictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-string">'1'</span>); 1200<span class="hljs-comment">// OK</span></code></pre> 1201<p>If the values are strictly equal, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a 1202<code>message</code> property set equal to the value of the <code>message</code> parameter. If the 1203<code>message</code> parameter is undefined, a default error message is assigned. If the 1204<code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown 1205instead of the <code>AssertionError</code>.</p> 1206</section><section><h3><code>assert.ok(value[, message])</code><span><a class="mark" href="#assert_assert_ok_value_message" id="assert_assert_ok_value_message">#</a></span></h3> 1207<div class="api_metadata"> 1208<details class="changelog"><summary>History</summary> 1209<table> 1210<tbody><tr><th>Version</th><th>Changes</th></tr> 1211<tr><td>v10.0.0</td> 1212<td><p>The <code>assert.ok()</code> (no arguments) will now use a predefined error message.</p></td></tr> 1213<tr><td>v0.1.21</td> 1214<td><p><span>Added in: v0.1.21</span></p></td></tr> 1215</tbody></table> 1216</details> 1217</div> 1218<ul> 1219<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 1220<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> 1221</ul> 1222<p>Tests if <code>value</code> is truthy. It is equivalent to 1223<code>assert.equal(!!value, true, message)</code>.</p> 1224<p>If <code>value</code> is not truthy, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code> 1225property set equal to the value of the <code>message</code> parameter. If the <code>message</code> 1226parameter is <code>undefined</code>, a default error message is assigned. If the <code>message</code> 1227parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the 1228<code>AssertionError</code>. 1229If no arguments are passed in at all <code>message</code> will be set to the string: 1230<code>'No value argument passed to `assert.ok()`'</code>.</p> 1231<p>Be aware that in the <code>repl</code> the error message will be different to the one 1232thrown in a file! See below for further details.</p> 1233<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>).<span class="hljs-property">strict</span>; 1234 1235assert.<span class="hljs-title function_">ok</span>(<span class="hljs-literal">true</span>); 1236<span class="hljs-comment">// OK</span> 1237assert.<span class="hljs-title function_">ok</span>(<span class="hljs-number">1</span>); 1238<span class="hljs-comment">// OK</span> 1239 1240assert.<span class="hljs-title function_">ok</span>(); 1241<span class="hljs-comment">// AssertionError: No value argument passed to `assert.ok()`</span> 1242 1243assert.<span class="hljs-title function_">ok</span>(<span class="hljs-literal">false</span>, <span class="hljs-string">'it\'s false'</span>); 1244<span class="hljs-comment">// AssertionError: it's false</span> 1245 1246<span class="hljs-comment">// In the repl:</span> 1247assert.<span class="hljs-title function_">ok</span>(<span class="hljs-keyword">typeof</span> <span class="hljs-number">123</span> === <span class="hljs-string">'string'</span>); 1248<span class="hljs-comment">// AssertionError: false == true</span> 1249 1250<span class="hljs-comment">// In a file (e.g. test.js):</span> 1251assert.<span class="hljs-title function_">ok</span>(<span class="hljs-keyword">typeof</span> <span class="hljs-number">123</span> === <span class="hljs-string">'string'</span>); 1252<span class="hljs-comment">// AssertionError: The expression evaluated to a falsy value:</span> 1253<span class="hljs-comment">//</span> 1254<span class="hljs-comment">// assert.ok(typeof 123 === 'string')</span> 1255 1256assert.<span class="hljs-title function_">ok</span>(<span class="hljs-literal">false</span>); 1257<span class="hljs-comment">// AssertionError: The expression evaluated to a falsy value:</span> 1258<span class="hljs-comment">//</span> 1259<span class="hljs-comment">// assert.ok(false)</span> 1260 1261assert.<span class="hljs-title function_">ok</span>(<span class="hljs-number">0</span>); 1262<span class="hljs-comment">// AssertionError: The expression evaluated to a falsy value:</span> 1263<span class="hljs-comment">//</span> 1264<span class="hljs-comment">// assert.ok(0)</span> 1265 1266<span class="hljs-comment">// Using `assert()` works the same:</span> 1267<span class="hljs-title function_">assert</span>(<span class="hljs-number">0</span>); 1268<span class="hljs-comment">// AssertionError: The expression evaluated to a falsy value:</span> 1269<span class="hljs-comment">//</span> 1270<span class="hljs-comment">// assert(0)</span></code></pre> 1271</section><section><h3><code>assert.rejects(asyncFn[, error][, message])</code><span><a class="mark" href="#assert_assert_rejects_asyncfn_error_message" id="assert_assert_rejects_asyncfn_error_message">#</a></span></h3> 1272<div class="api_metadata"> 1273<span>Added in: v10.0.0</span> 1274</div> 1275<ul> 1276<li><code>asyncFn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a></li> 1277<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> 1278<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 1279</ul> 1280<p>Awaits the <code>asyncFn</code> promise or, if <code>asyncFn</code> is a function, immediately 1281calls the function and awaits the returned promise to complete. It will then 1282check that the promise is rejected.</p> 1283<p>If <code>asyncFn</code> is a function and it throws an error synchronously, 1284<code>assert.rejects()</code> will return a rejected <code>Promise</code> with that error. If the 1285function does not return a promise, <code>assert.rejects()</code> will return a rejected 1286<code>Promise</code> with an <a href="errors.html#errors_err_invalid_return_value"><code>ERR_INVALID_RETURN_VALUE</code></a> error. In both cases the error 1287handler is skipped.</p> 1288<p>Besides the async nature to await the completion behaves identically to 1289<a href="#assert_assert_throws_fn_error_message"><code>assert.throws()</code></a>.</p> 1290<p>If specified, <code>error</code> can be a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes"><code>Class</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a>, a validation function, 1291an object where each property will be tested for, or an instance of error where 1292each property will be tested for including the non-enumerable <code>message</code> and 1293<code>name</code> properties.</p> 1294<p>If specified, <code>message</code> will be the message provided by the <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> 1295if the <code>asyncFn</code> fails to reject.</p> 1296<pre><code class="language-js">(<span class="hljs-keyword">async</span> () => { 1297 <span class="hljs-keyword">await</span> assert.<span class="hljs-title function_">rejects</span>( 1298 <span class="hljs-keyword">async</span> () => { 1299 <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>); 1300 }, 1301 { 1302 <span class="hljs-attr">name</span>: <span class="hljs-string">'TypeError'</span>, 1303 <span class="hljs-attr">message</span>: <span class="hljs-string">'Wrong value'</span> 1304 } 1305 ); 1306})();</code></pre> 1307<pre><code class="language-js">(<span class="hljs-keyword">async</span> () => { 1308 <span class="hljs-keyword">await</span> assert.<span class="hljs-title function_">rejects</span>( 1309 <span class="hljs-keyword">async</span> () => { 1310 <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>); 1311 }, 1312 <span class="hljs-function">(<span class="hljs-params">err</span>) =></span> { 1313 assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">name</span>, <span class="hljs-string">'TypeError'</span>); 1314 assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">message</span>, <span class="hljs-string">'Wrong value'</span>); 1315 <span class="hljs-keyword">return</span> <span class="hljs-literal">true</span>; 1316 } 1317 ); 1318})();</code></pre> 1319<pre><code class="language-js">assert.<span class="hljs-title function_">rejects</span>( 1320 <span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">reject</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Wrong value'</span>)), 1321 <span class="hljs-title class_">Error</span> 1322).<span class="hljs-title function_">then</span>(<span class="hljs-function">() =></span> { 1323 <span class="hljs-comment">// ...</span> 1324});</code></pre> 1325<p><code>error</code> cannot be a string. If a string is provided as the second 1326argument, then <code>error</code> is assumed to be omitted and the string will be used for 1327<code>message</code> instead. This can lead to easy-to-miss mistakes. Please read the 1328example in <a href="#assert_assert_throws_fn_error_message"><code>assert.throws()</code></a> carefully if using a string as the second 1329argument gets considered.</p> 1330</section><section><h3><code>assert.strictEqual(actual, expected[, message])</code><span><a class="mark" href="#assert_assert_strictequal_actual_expected_message" id="assert_assert_strictequal_actual_expected_message">#</a></span></h3> 1331<div class="api_metadata"> 1332<details class="changelog"><summary>History</summary> 1333<table> 1334<tbody><tr><th>Version</th><th>Changes</th></tr> 1335<tr><td>v10.0.0</td> 1336<td><p>Used comparison changed from Strict Equality to <code>Object.is()</code>.</p></td></tr> 1337<tr><td>v0.1.21</td> 1338<td><p><span>Added in: v0.1.21</span></p></td></tr> 1339</tbody></table> 1340</details> 1341</div> 1342<ul> 1343<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 1344<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 1345<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> 1346</ul> 1347<p>Tests strict equality between the <code>actual</code> and <code>expected</code> parameters as 1348determined by the <a href="https://tc39.github.io/ecma262/#sec-samevalue">SameValue Comparison</a>.</p> 1349<pre><code class="language-js"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'assert'</span>).<span class="hljs-property">strict</span>; 1350 1351assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>); 1352<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:</span> 1353<span class="hljs-comment">//</span> 1354<span class="hljs-comment">// 1 !== 2</span> 1355 1356assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>); 1357<span class="hljs-comment">// OK</span> 1358 1359assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-string">'Hello foobar'</span>, <span class="hljs-string">'Hello World!'</span>); 1360<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:</span> 1361<span class="hljs-comment">// + actual - expected</span> 1362<span class="hljs-comment">//</span> 1363<span class="hljs-comment">// + 'Hello foobar'</span> 1364<span class="hljs-comment">// - 'Hello World!'</span> 1365<span class="hljs-comment">// ^</span> 1366 1367<span class="hljs-keyword">const</span> apples = <span class="hljs-number">1</span>; 1368<span class="hljs-keyword">const</span> oranges = <span class="hljs-number">2</span>; 1369assert.<span class="hljs-title function_">strictEqual</span>(apples, oranges, <span class="hljs-string">`apples <span class="hljs-subst">${apples}</span> !== oranges <span class="hljs-subst">${oranges}</span>`</span>); 1370<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: apples 1 !== oranges 2</span> 1371 1372assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-string">'1'</span>, <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Inputs are not identical'</span>)); 1373<span class="hljs-comment">// TypeError: Inputs are not identical</span></code></pre> 1374<p>If the values are not strictly equal, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a 1375<code>message</code> property set equal to the value of the <code>message</code> parameter. If the 1376<code>message</code> parameter is undefined, a default error message is assigned. If the 1377<code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown 1378instead of the <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a>.</p> 1379</section><section><h3><code>assert.throws(fn[, error][, message])</code><span><a class="mark" href="#assert_assert_throws_fn_error_message" id="assert_assert_throws_fn_error_message">#</a></span></h3> 1380<div class="api_metadata"> 1381<details class="changelog"><summary>History</summary> 1382<table> 1383<tbody><tr><th>Version</th><th>Changes</th></tr> 1384<tr><td>v10.2.0</td> 1385<td><p>The <code>error</code> parameter can be an object containing regular expressions now.</p></td></tr> 1386<tr><td>v9.9.0</td> 1387<td><p>The <code>error</code> parameter can now be an object as well.</p></td></tr> 1388<tr><td>v4.2.0</td> 1389<td><p>The <code>error</code> parameter can now be an arrow function.</p></td></tr> 1390<tr><td>v0.1.21</td> 1391<td><p><span>Added in: v0.1.21</span></p></td></tr> 1392</tbody></table> 1393</details> 1394</div> 1395<ul> 1396<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> 1397<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> 1398<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 1399</ul> 1400<p>Expects the function <code>fn</code> to throw an error.</p> 1401<p>If specified, <code>error</code> can be a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes"><code>Class</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a>, a validation function, 1402a validation object where each property will be tested for strict deep equality, 1403or an instance of error where each property will be tested for strict deep 1404equality including the non-enumerable <code>message</code> and <code>name</code> properties. When 1405using an object, it is also possible to use a regular expression, when 1406validating against a string property. See below for examples.</p> 1407<p>If specified, <code>message</code> will be appended to the message provided by the 1408<code>AssertionError</code> if the <code>fn</code> call fails to throw or in case the error validation 1409fails.</p> 1410<p>Custom validation object/error instance:</p> 1411<pre><code class="language-js"><span class="hljs-keyword">const</span> err = <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>); 1412err.<span class="hljs-property">code</span> = <span class="hljs-number">404</span>; 1413err.<span class="hljs-property">foo</span> = <span class="hljs-string">'bar'</span>; 1414err.<span class="hljs-property">info</span> = { 1415 <span class="hljs-attr">nested</span>: <span class="hljs-literal">true</span>, 1416 <span class="hljs-attr">baz</span>: <span class="hljs-string">'text'</span> 1417}; 1418err.<span class="hljs-property">reg</span> = <span class="hljs-regexp">/abc/i</span>; 1419 1420assert.<span class="hljs-title function_">throws</span>( 1421 <span class="hljs-function">() =></span> { 1422 <span class="hljs-keyword">throw</span> err; 1423 }, 1424 { 1425 <span class="hljs-attr">name</span>: <span class="hljs-string">'TypeError'</span>, 1426 <span class="hljs-attr">message</span>: <span class="hljs-string">'Wrong value'</span>, 1427 <span class="hljs-attr">info</span>: { 1428 <span class="hljs-attr">nested</span>: <span class="hljs-literal">true</span>, 1429 <span class="hljs-attr">baz</span>: <span class="hljs-string">'text'</span> 1430 } 1431 <span class="hljs-comment">// Only properties on the validation object will be tested for.</span> 1432 <span class="hljs-comment">// Using nested objects requires all properties to be present. Otherwise</span> 1433 <span class="hljs-comment">// the validation is going to fail.</span> 1434 } 1435); 1436 1437<span class="hljs-comment">// Using regular expressions to validate error properties:</span> 1438assert.<span class="hljs-title function_">throws</span>( 1439 <span class="hljs-function">() =></span> { 1440 <span class="hljs-keyword">throw</span> err; 1441 }, 1442 { 1443 <span class="hljs-comment">// The `name` and `message` properties are strings and using regular</span> 1444 <span class="hljs-comment">// expressions on those will match against the string. If they fail, an</span> 1445 <span class="hljs-comment">// error is thrown.</span> 1446 <span class="hljs-attr">name</span>: <span class="hljs-regexp">/^TypeError$/</span>, 1447 <span class="hljs-attr">message</span>: <span class="hljs-regexp">/Wrong/</span>, 1448 <span class="hljs-attr">foo</span>: <span class="hljs-string">'bar'</span>, 1449 <span class="hljs-attr">info</span>: { 1450 <span class="hljs-attr">nested</span>: <span class="hljs-literal">true</span>, 1451 <span class="hljs-comment">// It is not possible to use regular expressions for nested properties!</span> 1452 <span class="hljs-attr">baz</span>: <span class="hljs-string">'text'</span> 1453 }, 1454 <span class="hljs-comment">// The `reg` property contains a regular expression and only if the</span> 1455 <span class="hljs-comment">// validation object contains an identical regular expression, it is going</span> 1456 <span class="hljs-comment">// to pass.</span> 1457 <span class="hljs-attr">reg</span>: <span class="hljs-regexp">/abc/i</span> 1458 } 1459); 1460 1461<span class="hljs-comment">// Fails due to the different `message` and `name` properties:</span> 1462assert.<span class="hljs-title function_">throws</span>( 1463 <span class="hljs-function">() =></span> { 1464 <span class="hljs-keyword">const</span> otherErr = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Not found'</span>); 1465 <span class="hljs-comment">// Copy all enumerable properties from `err` to `otherErr`.</span> 1466 <span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> [key, value] <span class="hljs-keyword">of</span> <span class="hljs-title class_">Object</span>.<span class="hljs-title function_">entries</span>(err)) { 1467 otherErr[key] = value; 1468 } 1469 <span class="hljs-keyword">throw</span> otherErr; 1470 }, 1471 <span class="hljs-comment">// The error's `message` and `name` properties will also be checked when using</span> 1472 <span class="hljs-comment">// an error as validation object.</span> 1473 err 1474);</code></pre> 1475<p>Validate instanceof using constructor:</p> 1476<pre><code class="language-js">assert.<span class="hljs-title function_">throws</span>( 1477 <span class="hljs-function">() =></span> { 1478 <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Wrong value'</span>); 1479 }, 1480 <span class="hljs-title class_">Error</span> 1481);</code></pre> 1482<p>Validate error message using <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a>:</p> 1483<p>Using a regular expression runs <code>.toString</code> on the error object, and will 1484therefore also include the error name.</p> 1485<pre><code class="language-js">assert.<span class="hljs-title function_">throws</span>( 1486 <span class="hljs-function">() =></span> { 1487 <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Wrong value'</span>); 1488 }, 1489 <span class="hljs-regexp">/^Error: Wrong value$/</span> 1490);</code></pre> 1491<p>Custom error validation:</p> 1492<p>The function must return <code>true</code> to indicate all internal validations passed. 1493It will otherwise fail with an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a>.</p> 1494<pre><code class="language-js">assert.<span class="hljs-title function_">throws</span>( 1495 <span class="hljs-function">() =></span> { 1496 <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Wrong value'</span>); 1497 }, 1498 <span class="hljs-function">(<span class="hljs-params">err</span>) =></span> { 1499 <span class="hljs-title function_">assert</span>(err <span class="hljs-keyword">instanceof</span> <span class="hljs-title class_">Error</span>); 1500 <span class="hljs-title function_">assert</span>(<span class="hljs-regexp">/value/</span>.<span class="hljs-title function_">test</span>(err)); 1501 <span class="hljs-comment">// Avoid returning anything from validation functions besides `true`.</span> 1502 <span class="hljs-comment">// Otherwise, it's not clear what part of the validation failed. Instead,</span> 1503 <span class="hljs-comment">// throw an error about the specific validation that failed (as done in this</span> 1504 <span class="hljs-comment">// example) and add as much helpful debugging information to that error as</span> 1505 <span class="hljs-comment">// possible.</span> 1506 <span class="hljs-keyword">return</span> <span class="hljs-literal">true</span>; 1507 }, 1508 <span class="hljs-string">'unexpected error'</span> 1509);</code></pre> 1510<p><code>error</code> cannot be a string. If a string is provided as the second 1511argument, then <code>error</code> is assumed to be omitted and the string will be used for 1512<code>message</code> instead. This can lead to easy-to-miss mistakes. Using the same 1513message as the thrown error message is going to result in an 1514<code>ERR_AMBIGUOUS_ARGUMENT</code> error. Please read the example below carefully if using 1515a string as the second argument gets considered:</p> 1516<!-- eslint-disable no-restricted-syntax --> 1517<pre><code class="language-js"><span class="hljs-keyword">function</span> <span class="hljs-title function_">throwingFirst</span>(<span class="hljs-params"></span>) { 1518 <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'First'</span>); 1519} 1520 1521<span class="hljs-keyword">function</span> <span class="hljs-title function_">throwingSecond</span>(<span class="hljs-params"></span>) { 1522 <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Second'</span>); 1523} 1524 1525<span class="hljs-keyword">function</span> <span class="hljs-title function_">notThrowing</span>(<span class="hljs-params"></span>) {} 1526 1527<span class="hljs-comment">// The second argument is a string and the input function threw an Error.</span> 1528<span class="hljs-comment">// The first case will not throw as it does not match for the error message</span> 1529<span class="hljs-comment">// thrown by the input function!</span> 1530assert.<span class="hljs-title function_">throws</span>(throwingFirst, <span class="hljs-string">'Second'</span>); 1531<span class="hljs-comment">// In the next example the message has no benefit over the message from the</span> 1532<span class="hljs-comment">// error and since it is not clear if the user intended to actually match</span> 1533<span class="hljs-comment">// against the error message, Node.js throws an `ERR_AMBIGUOUS_ARGUMENT` error.</span> 1534assert.<span class="hljs-title function_">throws</span>(throwingSecond, <span class="hljs-string">'Second'</span>); 1535<span class="hljs-comment">// TypeError [ERR_AMBIGUOUS_ARGUMENT]</span> 1536 1537<span class="hljs-comment">// The string is only used (as message) in case the function does not throw:</span> 1538assert.<span class="hljs-title function_">throws</span>(notThrowing, <span class="hljs-string">'Second'</span>); 1539<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Missing expected exception: Second</span> 1540 1541<span class="hljs-comment">// If it was intended to match for the error message do this instead:</span> 1542<span class="hljs-comment">// It does not throw because the error messages match.</span> 1543assert.<span class="hljs-title function_">throws</span>(throwingSecond, <span class="hljs-regexp">/Second$/</span>); 1544 1545<span class="hljs-comment">// If the error message does not match, an AssertionError is thrown.</span> 1546assert.<span class="hljs-title function_">throws</span>(throwingFirst, <span class="hljs-regexp">/Second$/</span>); 1547<span class="hljs-comment">// AssertionError [ERR_ASSERTION]</span></code></pre> 1548<p>Due to the confusing error-prone notation, avoid a string as the second 1549argument.</p></section> 1550 <!-- API END --> 1551 </div> 1552 </div> 1553 </div> 1554 <script> 1555 'use strict'; 1556 { 1557 const kCustomPreference = 'customDarkTheme'; 1558 const userSettings = sessionStorage.getItem(kCustomPreference); 1559 const themeToggleButton = document.getElementById('theme-toggle-btn'); 1560 if (userSettings === null && window.matchMedia) { 1561 const mq = window.matchMedia('(prefers-color-scheme: dark)'); 1562 if ('onchange' in mq) { 1563 function mqChangeListener(e) { 1564 document.body.classList.toggle('dark-mode', e.matches); 1565 } 1566 mq.addEventListener('change', mqChangeListener); 1567 if (themeToggleButton) { 1568 themeToggleButton.addEventListener('click', function() { 1569 mq.removeEventListener('change', mqChangeListener); 1570 }, { once: true }); 1571 } 1572 } 1573 if (mq.matches) { 1574 document.body.classList.add('dark-mode'); 1575 } 1576 } else if (userSettings === 'true') { 1577 document.body.classList.add('dark-mode'); 1578 } 1579 if (themeToggleButton) { 1580 themeToggleButton.hidden = false; 1581 themeToggleButton.addEventListener('click', function() { 1582 sessionStorage.setItem( 1583 kCustomPreference, 1584 document.body.classList.toggle('dark-mode') 1585 ); 1586 }); 1587 } 1588 } 1589 </script> 1590</body> 1591</html> 1592