1<!DOCTYPE html> 2<html lang="en"> 3<head> 4 <meta charset="utf-8"> 5 <meta name="viewport" content="width=device-width"> 6 <meta name="nodejs.org:node-version" content="v14.19.1"> 7 <title>Readline | Node.js v14.19.1 Documentation</title> 8 <link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Lato:400,700,400italic&display=fallback"> 9 <link rel="stylesheet" href="assets/style.css"> 10 <link rel="stylesheet" href="assets/hljs.css"> 11 <link rel="canonical" href="https://nodejs.org/api/readline.html"> 12</head> 13<body class="alt apidoc" id="api-section-readline"> 14 <div id="content" class="clearfix"> 15 <div id="column2" class="interior"> 16 <div id="intro" class="interior"> 17 <a href="/" title="Go back to the home page"> 18 Node.js 19 </a> 20 </div> 21 <ul> 22<li><a href="documentation.html" class="nav-documentation">About this documentation</a></li> 23<li><a href="synopsis.html" class="nav-synopsis">Usage and example</a></li> 24</ul> 25<hr class="line"> 26<ul> 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<div id="column1" data-id="readline" class="interior"> 90 <header> 91 <div class="header-container"> 92 <h1>Node.js v14.19.1 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 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href="https://nodejs.org/docs/latest-v14.x/api/readline.html">14.x <b>LTS</b></a></li> 123<li><a href="https://nodejs.org/docs/latest-v13.x/api/readline.html">13.x</a></li> 124<li><a href="https://nodejs.org/docs/latest-v12.x/api/readline.html">12.x <b>LTS</b></a></li> 125<li><a href="https://nodejs.org/docs/latest-v11.x/api/readline.html">11.x</a></li> 126<li><a href="https://nodejs.org/docs/latest-v10.x/api/readline.html">10.x</a></li> 127<li><a href="https://nodejs.org/docs/latest-v9.x/api/readline.html">9.x</a></li> 128<li><a href="https://nodejs.org/docs/latest-v8.x/api/readline.html">8.x</a></li> 129<li><a href="https://nodejs.org/docs/latest-v7.x/api/readline.html">7.x</a></li> 130<li><a href="https://nodejs.org/docs/latest-v6.x/api/readline.html">6.x</a></li> 131<li><a href="https://nodejs.org/docs/latest-v5.x/api/readline.html">5.x</a></li> 132<li><a href="https://nodejs.org/docs/latest-v4.x/api/readline.html">4.x</a></li> 133<li><a href="https://nodejs.org/docs/latest-v0.12.x/api/readline.html">0.12.x</a></li> 134<li><a href="https://nodejs.org/docs/latest-v0.10.x/api/readline.html">0.10.x</a></li></ol> 135 </li> 136 137 <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/master/doc/api/readline.md">Edit on GitHub</a></li> 138 </ul> 139 </div> 140 <hr> 141 </header> 142 143 <details id="toc" open><summary>Table of contents</summary><ul> 144<li><span class="stability_2"><a href="#readline_readline">Readline</a></span> 145<ul> 146<li><a href="#readline_class_interface">Class: <code>Interface</code></a> 147<ul> 148<li><a href="#readline_event_close">Event: <code>'close'</code></a></li> 149<li><a href="#readline_event_line">Event: <code>'line'</code></a></li> 150<li><a href="#readline_event_history">Event: <code>'history'</code></a></li> 151<li><a href="#readline_event_pause">Event: <code>'pause'</code></a></li> 152<li><a href="#readline_event_resume">Event: <code>'resume'</code></a></li> 153<li><a href="#readline_event_sigcont">Event: <code>'SIGCONT'</code></a></li> 154<li><a href="#readline_event_sigint">Event: <code>'SIGINT'</code></a></li> 155<li><a href="#readline_event_sigtstp">Event: <code>'SIGTSTP'</code></a></li> 156<li><a href="#readline_rl_close"><code>rl.close()</code></a></li> 157<li><a href="#readline_rl_pause"><code>rl.pause()</code></a></li> 158<li><a href="#readline_rl_prompt_preservecursor"><code>rl.prompt([preserveCursor])</code></a></li> 159<li><a href="#readline_rl_question_query_options_callback"><code>rl.question(query[, options], callback)</code></a></li> 160<li><a href="#readline_rl_resume"><code>rl.resume()</code></a></li> 161<li><a href="#readline_rl_setprompt_prompt"><code>rl.setPrompt(prompt)</code></a></li> 162<li><a href="#readline_rl_getprompt"><code>rl.getPrompt()</code></a></li> 163<li><a href="#readline_rl_write_data_key"><code>rl.write(data[, key])</code></a></li> 164<li><a href="#readline_rl_symbol_asynciterator"><code>rl[Symbol.asyncIterator]()</code></a></li> 165<li><a href="#readline_rl_line"><code>rl.line</code></a></li> 166<li><a href="#readline_rl_cursor"><code>rl.cursor</code></a></li> 167<li><a href="#readline_rl_getcursorpos"><code>rl.getCursorPos()</code></a></li> 168</ul> 169</li> 170<li><a href="#readline_readline_clearline_stream_dir_callback"><code>readline.clearLine(stream, dir[, callback])</code></a></li> 171<li><a href="#readline_readline_clearscreendown_stream_callback"><code>readline.clearScreenDown(stream[, callback])</code></a></li> 172<li><a href="#readline_readline_createinterface_options"><code>readline.createInterface(options)</code></a> 173<ul> 174<li><a href="#readline_use_of_the_completer_function">Use of the <code>completer</code> function</a></li> 175</ul> 176</li> 177<li><a href="#readline_readline_cursorto_stream_x_y_callback"><code>readline.cursorTo(stream, x[, y][, callback])</code></a></li> 178<li><a href="#readline_readline_emitkeypressevents_stream_interface"><code>readline.emitKeypressEvents(stream[, interface])</code></a></li> 179<li><a href="#readline_readline_movecursor_stream_dx_dy_callback"><code>readline.moveCursor(stream, dx, dy[, callback])</code></a></li> 180<li><a href="#readline_example_tiny_cli">Example: Tiny CLI</a></li> 181<li><a href="#readline_example_read_file_stream_line_by_line">Example: Read file stream line-by-Line</a></li> 182<li><a href="#readline_tty_keybindings">TTY keybindings</a></li> 183</ul> 184</li> 185</ul></details> 186 187 <div id="apicontent"> 188 <h2>Readline<span><a class="mark" href="#readline_readline" id="readline_readline">#</a></span></h2> 189 190<p></p><div class="api_stability api_stability_2"><a href="documentation.html#documentation_stability_index">Stability: 2</a> - Stable</div><p></p> 191<p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v14.19.1/lib/readline.js">lib/readline.js</a></p> 192<p>The <code>readline</code> module provides an interface for reading data from a <a href="stream.html#stream_readable_streams">Readable</a> 193stream (such as <a href="process.html#process_process_stdin"><code>process.stdin</code></a>) one line at a time. It can be accessed 194using:</p> 195<pre><code class="language-js"><span class="hljs-keyword">const</span> readline = <span class="hljs-built_in">require</span>(<span class="hljs-string">'readline'</span>);</code></pre> 196<p>The following simple example illustrates the basic use of the <code>readline</code> module.</p> 197<pre><code class="language-js"><span class="hljs-keyword">const</span> readline = <span class="hljs-built_in">require</span>(<span class="hljs-string">'readline'</span>); 198 199<span class="hljs-keyword">const</span> rl = readline.<span class="hljs-title function_">createInterface</span>({ 200 <span class="hljs-attr">input</span>: process.<span class="hljs-property">stdin</span>, 201 <span class="hljs-attr">output</span>: process.<span class="hljs-property">stdout</span> 202}); 203 204rl.<span class="hljs-title function_">question</span>(<span class="hljs-string">'What do you think of Node.js? '</span>, <span class="hljs-function">(<span class="hljs-params">answer</span>) =></span> { 205 <span class="hljs-comment">// <span class="hljs-doctag">TODO:</span> Log the answer in a database</span> 206 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Thank you for your valuable feedback: <span class="hljs-subst">${answer}</span>`</span>); 207 208 rl.<span class="hljs-title function_">close</span>(); 209});</code></pre> 210<p>Once this code is invoked, the Node.js application will not terminate until the 211<code>readline.Interface</code> is closed because the interface waits for data to be 212received on the <code>input</code> stream.</p> 213<section><h3>Class: <code>Interface</code><span><a class="mark" href="#readline_class_interface" id="readline_class_interface">#</a></span></h3> 214<div class="api_metadata"> 215<span>Added in: v0.1.104</span> 216</div> 217<ul> 218<li>Extends: <a href="events.html#events_class_eventemitter" class="type"><EventEmitter></a></li> 219</ul> 220<p>Instances of the <code>readline.Interface</code> class are constructed using the 221<code>readline.createInterface()</code> method. Every instance is associated with a 222single <code>input</code> <a href="stream.html#stream_readable_streams">Readable</a> stream and a single <code>output</code> <a href="stream.html#stream_writable_streams">Writable</a> stream. 223The <code>output</code> stream is used to print prompts for user input that arrives on, 224and is read from, the <code>input</code> stream.</p> 225<h4>Event: <code>'close'</code><span><a class="mark" href="#readline_event_close" id="readline_event_close">#</a></span></h4> 226<div class="api_metadata"> 227<span>Added in: v0.1.98</span> 228</div> 229<p>The <code>'close'</code> event is emitted when one of the following occur:</p> 230<ul> 231<li>The <code>rl.close()</code> method is called and the <code>readline.Interface</code> instance has 232relinquished control over the <code>input</code> and <code>output</code> streams;</li> 233<li>The <code>input</code> stream receives its <code>'end'</code> event;</li> 234<li>The <code>input</code> stream receives <kbd>Ctrl</kbd>+<kbd>D</kbd> to signal 235end-of-transmission (EOT);</li> 236<li>The <code>input</code> stream receives <kbd>Ctrl</kbd>+<kbd>C</kbd> to signal <code>SIGINT</code> 237and there is no <code>'SIGINT'</code> event listener registered on the 238<code>readline.Interface</code> instance.</li> 239</ul> 240<p>The listener function is called without passing any arguments.</p> 241<p>The <code>readline.Interface</code> instance is finished once the <code>'close'</code> event is 242emitted.</p> 243<h4>Event: <code>'line'</code><span><a class="mark" href="#readline_event_line" id="readline_event_line">#</a></span></h4> 244<div class="api_metadata"> 245<span>Added in: v0.1.98</span> 246</div> 247<p>The <code>'line'</code> event is emitted whenever the <code>input</code> stream receives an 248end-of-line input (<code>\n</code>, <code>\r</code>, or <code>\r\n</code>). This usually occurs when the user 249presses <kbd>Enter</kbd> or <kbd>Return</kbd>.</p> 250<p>The listener function is called with a string containing the single line of 251received input.</p> 252<pre><code class="language-js">rl.<span class="hljs-title function_">on</span>(<span class="hljs-string">'line'</span>, <span class="hljs-function">(<span class="hljs-params">input</span>) =></span> { 253 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Received: <span class="hljs-subst">${input}</span>`</span>); 254});</code></pre> 255<h4>Event: <code>'history'</code><span><a class="mark" href="#readline_event_history" id="readline_event_history">#</a></span></h4> 256<div class="api_metadata"> 257<span>Added in: v14.18.0</span> 258</div> 259<p>The <code>'history'</code> event is emitted whenever the history array has changed.</p> 260<p>The listener function is called with an array containing the history array. 261It will reflect all changes, added lines and removed lines due to 262<code>historySize</code> and <code>removeHistoryDuplicates</code>.</p> 263<p>The primary purpose is to allow a listener to persist the history. 264It is also possible for the listener to change the history object. This 265could be useful to prevent certain lines to be added to the history, like 266a password.</p> 267<pre><code class="language-js">rl.<span class="hljs-title function_">on</span>(<span class="hljs-string">'history'</span>, <span class="hljs-function">(<span class="hljs-params">history</span>) =></span> { 268 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Received: <span class="hljs-subst">${history}</span>`</span>); 269});</code></pre> 270<h4>Event: <code>'pause'</code><span><a class="mark" href="#readline_event_pause" id="readline_event_pause">#</a></span></h4> 271<div class="api_metadata"> 272<span>Added in: v0.7.5</span> 273</div> 274<p>The <code>'pause'</code> event is emitted when one of the following occur:</p> 275<ul> 276<li>The <code>input</code> stream is paused.</li> 277<li>The <code>input</code> stream is not paused and receives the <code>'SIGCONT'</code> event. (See 278events <a href="#readline_event_sigtstp"><code>'SIGTSTP'</code></a> and <a href="#readline_event_sigcont"><code>'SIGCONT'</code></a>.)</li> 279</ul> 280<p>The listener function is called without passing any arguments.</p> 281<pre><code class="language-js">rl.<span class="hljs-title function_">on</span>(<span class="hljs-string">'pause'</span>, <span class="hljs-function">() =></span> { 282 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'Readline paused.'</span>); 283});</code></pre> 284<h4>Event: <code>'resume'</code><span><a class="mark" href="#readline_event_resume" id="readline_event_resume">#</a></span></h4> 285<div class="api_metadata"> 286<span>Added in: v0.7.5</span> 287</div> 288<p>The <code>'resume'</code> event is emitted whenever the <code>input</code> stream is resumed.</p> 289<p>The listener function is called without passing any arguments.</p> 290<pre><code class="language-js">rl.<span class="hljs-title function_">on</span>(<span class="hljs-string">'resume'</span>, <span class="hljs-function">() =></span> { 291 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'Readline resumed.'</span>); 292});</code></pre> 293<h4>Event: <code>'SIGCONT'</code><span><a class="mark" href="#readline_event_sigcont" id="readline_event_sigcont">#</a></span></h4> 294<div class="api_metadata"> 295<span>Added in: v0.7.5</span> 296</div> 297<p>The <code>'SIGCONT'</code> event is emitted when a Node.js process previously moved into 298the background using <kbd>Ctrl</kbd>+<kbd>Z</kbd> (i.e. <code>SIGTSTP</code>) is then 299brought back to the foreground using <a href="http://man7.org/linux/man-pages/man1/fg.1p.html"><code>fg(1p)</code></a>.</p> 300<p>If the <code>input</code> stream was paused <em>before</em> the <code>SIGTSTP</code> request, this event will 301not be emitted.</p> 302<p>The listener function is invoked without passing any arguments.</p> 303<pre><code class="language-js">rl.<span class="hljs-title function_">on</span>(<span class="hljs-string">'SIGCONT'</span>, <span class="hljs-function">() =></span> { 304 <span class="hljs-comment">// `prompt` will automatically resume the stream</span> 305 rl.<span class="hljs-title function_">prompt</span>(); 306});</code></pre> 307<p>The <code>'SIGCONT'</code> event is <em>not</em> supported on Windows.</p> 308<h4>Event: <code>'SIGINT'</code><span><a class="mark" href="#readline_event_sigint" id="readline_event_sigint">#</a></span></h4> 309<div class="api_metadata"> 310<span>Added in: v0.3.0</span> 311</div> 312<p>The <code>'SIGINT'</code> event is emitted whenever the <code>input</code> stream receives a 313<kbd>Ctrl+C</kbd> input, known typically as <code>SIGINT</code>. If there are no <code>'SIGINT'</code> 314event listeners registered when the <code>input</code> stream receives a <code>SIGINT</code>, the 315<code>'pause'</code> event will be emitted.</p> 316<p>The listener function is invoked without passing any arguments.</p> 317<pre><code class="language-js">rl.<span class="hljs-title function_">on</span>(<span class="hljs-string">'SIGINT'</span>, <span class="hljs-function">() =></span> { 318 rl.<span class="hljs-title function_">question</span>(<span class="hljs-string">'Are you sure you want to exit? '</span>, <span class="hljs-function">(<span class="hljs-params">answer</span>) =></span> { 319 <span class="hljs-keyword">if</span> (answer.<span class="hljs-title function_">match</span>(<span class="hljs-regexp">/^y(es)?$/i</span>)) rl.<span class="hljs-title function_">pause</span>(); 320 }); 321});</code></pre> 322<h4>Event: <code>'SIGTSTP'</code><span><a class="mark" href="#readline_event_sigtstp" id="readline_event_sigtstp">#</a></span></h4> 323<div class="api_metadata"> 324<span>Added in: v0.7.5</span> 325</div> 326<p>The <code>'SIGTSTP'</code> event is emitted when the <code>input</code> stream receives a 327<kbd>Ctrl</kbd>+<kbd>Z</kbd> input, typically known as <code>SIGTSTP</code>. If there are 328no <code>'SIGTSTP'</code> event listeners registered when the <code>input</code> stream receives a 329<code>SIGTSTP</code>, the Node.js process will be sent to the background.</p> 330<p>When the program is resumed using <a href="http://man7.org/linux/man-pages/man1/fg.1p.html"><code>fg(1p)</code></a>, the <code>'pause'</code> and <code>'SIGCONT'</code> events 331will be emitted. These can be used to resume the <code>input</code> stream.</p> 332<p>The <code>'pause'</code> and <code>'SIGCONT'</code> events will not be emitted if the <code>input</code> was 333paused before the process was sent to the background.</p> 334<p>The listener function is invoked without passing any arguments.</p> 335<pre><code class="language-js">rl.<span class="hljs-title function_">on</span>(<span class="hljs-string">'SIGTSTP'</span>, <span class="hljs-function">() =></span> { 336 <span class="hljs-comment">// This will override SIGTSTP and prevent the program from going to the</span> 337 <span class="hljs-comment">// background.</span> 338 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'Caught SIGTSTP.'</span>); 339});</code></pre> 340<p>The <code>'SIGTSTP'</code> event is <em>not</em> supported on Windows.</p> 341<h4><code>rl.close()</code><span><a class="mark" href="#readline_rl_close" id="readline_rl_close">#</a></span></h4> 342<div class="api_metadata"> 343<span>Added in: v0.1.98</span> 344</div> 345<p>The <code>rl.close()</code> method closes the <code>readline.Interface</code> instance and 346relinquishes control over the <code>input</code> and <code>output</code> streams. When called, 347the <code>'close'</code> event will be emitted.</p> 348<p>Calling <code>rl.close()</code> does not immediately stop other events (including <code>'line'</code>) 349from being emitted by the <code>readline.Interface</code> instance.</p> 350<h4><code>rl.pause()</code><span><a class="mark" href="#readline_rl_pause" id="readline_rl_pause">#</a></span></h4> 351<div class="api_metadata"> 352<span>Added in: v0.3.4</span> 353</div> 354<p>The <code>rl.pause()</code> method pauses the <code>input</code> stream, allowing it to be resumed 355later if necessary.</p> 356<p>Calling <code>rl.pause()</code> does not immediately pause other events (including 357<code>'line'</code>) from being emitted by the <code>readline.Interface</code> instance.</p> 358<h4><code>rl.prompt([preserveCursor])</code><span><a class="mark" href="#readline_rl_prompt_preservecursor" id="readline_rl_prompt_preservecursor">#</a></span></h4> 359<div class="api_metadata"> 360<span>Added in: v0.1.98</span> 361</div> 362<ul> 363<li><code>preserveCursor</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>true</code>, prevents the cursor placement from 364being reset to <code>0</code>.</li> 365</ul> 366<p>The <code>rl.prompt()</code> method writes the <code>readline.Interface</code> instances configured 367<code>prompt</code> to a new line in <code>output</code> in order to provide a user with a new 368location at which to provide input.</p> 369<p>When called, <code>rl.prompt()</code> will resume the <code>input</code> stream if it has been 370paused.</p> 371<p>If the <code>readline.Interface</code> was created with <code>output</code> set to <code>null</code> or 372<code>undefined</code> the prompt is not written.</p> 373<h4><code>rl.question(query[, options], callback)</code><span><a class="mark" href="#readline_rl_question_query_options_callback" id="readline_rl_question_query_options_callback">#</a></span></h4> 374<div class="api_metadata"> 375<span>Added in: v0.3.3</span> 376</div> 377<ul> 378<li><code>query</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A statement or query to write to <code>output</code>, prepended to the 379prompt.</li> 380<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 381<ul> 382<li><code>signal</code> <a href="globals.html#globals_class_abortsignal" class="type"><AbortSignal></a> Optionally allows the <code>question()</code> to be canceled 383using an <code>AbortController</code>.</li> 384</ul> 385</li> 386<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A callback function that is invoked with the user's 387input in response to the <code>query</code>.</li> 388</ul> 389<p>The <code>rl.question()</code> method displays the <code>query</code> by writing it to the <code>output</code>, 390waits for user input to be provided on <code>input</code>, then invokes the <code>callback</code> 391function passing the provided input as the first argument.</p> 392<p>When called, <code>rl.question()</code> will resume the <code>input</code> stream if it has been 393paused.</p> 394<p>If the <code>readline.Interface</code> was created with <code>output</code> set to <code>null</code> or 395<code>undefined</code> the <code>query</code> is not written.</p> 396<p>The <code>callback</code> function passed to <code>rl.question()</code> does not follow the typical 397pattern of accepting an <code>Error</code> object or <code>null</code> as the first argument. 398The <code>callback</code> is called with the provided answer as the only argument.</p> 399<p>Example usage:</p> 400<pre><code class="language-js">rl.<span class="hljs-title function_">question</span>(<span class="hljs-string">'What is your favorite food? '</span>, <span class="hljs-function">(<span class="hljs-params">answer</span>) =></span> { 401 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Oh, so your favorite food is <span class="hljs-subst">${answer}</span>`</span>); 402});</code></pre> 403<p>Using an <code>AbortController</code> to cancel a question.</p> 404<pre><code class="language-js"><span class="hljs-keyword">const</span> ac = <span class="hljs-keyword">new</span> <span class="hljs-title class_">AbortController</span>(); 405<span class="hljs-keyword">const</span> signal = ac.<span class="hljs-property">signal</span>; 406 407rl.<span class="hljs-title function_">question</span>(<span class="hljs-string">'What is your favorite food? '</span>, { signal }, <span class="hljs-function">(<span class="hljs-params">answer</span>) =></span> { 408 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Oh, so your favorite food is <span class="hljs-subst">${answer}</span>`</span>); 409}); 410 411signal.<span class="hljs-title function_">addEventListener</span>(<span class="hljs-string">'abort'</span>, <span class="hljs-function">() =></span> { 412 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'The food question timed out'</span>); 413}, { <span class="hljs-attr">once</span>: <span class="hljs-literal">true</span> }); 414 415<span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> ac.<span class="hljs-title function_">abort</span>(), <span class="hljs-number">10000</span>);</code></pre> 416<p>If this method is invoked as it's util.promisify()ed version, it returns a 417Promise that fulfills with the answer. If the question is canceled using 418an <code>AbortController</code> it will reject with an <code>AbortError</code>.</p> 419<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'util'</span>); 420<span class="hljs-keyword">const</span> question = util.<span class="hljs-title function_">promisify</span>(rl.<span class="hljs-property">question</span>).<span class="hljs-title function_">bind</span>(rl); 421 422<span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">questionExample</span>(<span class="hljs-params"></span>) { 423 <span class="hljs-keyword">try</span> { 424 <span class="hljs-keyword">const</span> answer = <span class="hljs-keyword">await</span> <span class="hljs-title function_">question</span>(<span class="hljs-string">'What is you favorite food? '</span>); 425 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Oh, so your favorite food is <span class="hljs-subst">${answer}</span>`</span>); 426 } <span class="hljs-keyword">catch</span> (err) { 427 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">error</span>(<span class="hljs-string">'Question rejected'</span>, err); 428 } 429} 430<span class="hljs-title function_">questionExample</span>();</code></pre> 431<h4><code>rl.resume()</code><span><a class="mark" href="#readline_rl_resume" id="readline_rl_resume">#</a></span></h4> 432<div class="api_metadata"> 433<span>Added in: v0.3.4</span> 434</div> 435<p>The <code>rl.resume()</code> method resumes the <code>input</code> stream if it has been paused.</p> 436<h4><code>rl.setPrompt(prompt)</code><span><a class="mark" href="#readline_rl_setprompt_prompt" id="readline_rl_setprompt_prompt">#</a></span></h4> 437<div class="api_metadata"> 438<span>Added in: v0.1.98</span> 439</div> 440<ul> 441<li><code>prompt</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 442</ul> 443<p>The <code>rl.setPrompt()</code> method sets the prompt that will be written to <code>output</code> 444whenever <code>rl.prompt()</code> is called.</p> 445<h4><code>rl.getPrompt()</code><span><a class="mark" href="#readline_rl_getprompt" id="readline_rl_getprompt">#</a></span></h4> 446<div class="api_metadata"> 447<span>Added in: v14.17.0</span> 448</div> 449<ul> 450<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> the current prompt string</li> 451</ul> 452<p>The <code>rl.getPrompt()</code> method returns the current prompt used by <code>rl.prompt()</code>.</p> 453<h4><code>rl.write(data[, key])</code><span><a class="mark" href="#readline_rl_write_data_key" id="readline_rl_write_data_key">#</a></span></h4> 454<div class="api_metadata"> 455<span>Added in: v0.1.98</span> 456</div> 457<ul> 458<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 459<li><code>key</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 460<ul> 461<li><code>ctrl</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> to indicate the <kbd>Ctrl</kbd> key.</li> 462<li><code>meta</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> to indicate the <kbd>Meta</kbd> key.</li> 463<li><code>shift</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> to indicate the <kbd>Shift</kbd> key.</li> 464<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The name of the a key.</li> 465</ul> 466</li> 467</ul> 468<p>The <code>rl.write()</code> method will write either <code>data</code> or a key sequence identified 469by <code>key</code> to the <code>output</code>. The <code>key</code> argument is supported only if <code>output</code> is 470a <a href="tty.html">TTY</a> text terminal. See <a href="#readline_tty_keybindings">TTY keybindings</a> for a list of key 471combinations.</p> 472<p>If <code>key</code> is specified, <code>data</code> is ignored.</p> 473<p>When called, <code>rl.write()</code> will resume the <code>input</code> stream if it has been 474paused.</p> 475<p>If the <code>readline.Interface</code> was created with <code>output</code> set to <code>null</code> or 476<code>undefined</code> the <code>data</code> and <code>key</code> are not written.</p> 477<pre><code class="language-js">rl.<span class="hljs-title function_">write</span>(<span class="hljs-string">'Delete this!'</span>); 478<span class="hljs-comment">// Simulate Ctrl+U to delete the line written previously</span> 479rl.<span class="hljs-title function_">write</span>(<span class="hljs-literal">null</span>, { <span class="hljs-attr">ctrl</span>: <span class="hljs-literal">true</span>, <span class="hljs-attr">name</span>: <span class="hljs-string">'u'</span> });</code></pre> 480<p>The <code>rl.write()</code> method will write the data to the <code>readline</code> <code>Interface</code>'s 481<code>input</code> <em>as if it were provided by the user</em>.</p> 482<h4><code>rl[Symbol.asyncIterator]()</code><span><a class="mark" href="#readline_rl_symbol_asynciterator" id="readline_rl_symbol_asynciterator">#</a></span></h4> 483<div class="api_metadata"> 484<details class="changelog"><summary>History</summary> 485<table> 486<tbody><tr><th>Version</th><th>Changes</th></tr> 487<tr><td>v11.4.0, v10.16.0</td> 488<td><p><span>Added in: v11.4.0, v10.16.0</span></p></td></tr> 489<tr><td>v11.14.0, v10.17.0</td> 490<td><p>Symbol.asyncIterator support is no longer experimental.</p></td></tr> 491</tbody></table> 492</details> 493</div> 494<ul> 495<li>Returns: <a href="https://tc39.github.io/ecma262/#sec-asynciterator-interface" class="type"><AsyncIterator></a></li> 496</ul> 497<p>Create an <code>AsyncIterator</code> object that iterates through each line in the input 498stream as a string. This method allows asynchronous iteration of 499<code>readline.Interface</code> objects through <code>for await...of</code> loops.</p> 500<p>Errors in the input stream are not forwarded.</p> 501<p>If the loop is terminated with <code>break</code>, <code>throw</code>, or <code>return</code>, 502<a href="#readline_rl_close"><code>rl.close()</code></a> will be called. In other words, iterating over a 503<code>readline.Interface</code> will always consume the input stream fully.</p> 504<p>Performance is not on par with the traditional <code>'line'</code> event API. Use <code>'line'</code> 505instead for performance-sensitive applications.</p> 506<pre><code class="language-js"><span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">processLineByLine</span>(<span class="hljs-params"></span>) { 507 <span class="hljs-keyword">const</span> rl = readline.<span class="hljs-title function_">createInterface</span>({ 508 <span class="hljs-comment">// ...</span> 509 }); 510 511 <span class="hljs-keyword">for</span> <span class="hljs-keyword">await</span> (<span class="hljs-keyword">const</span> line <span class="hljs-keyword">of</span> rl) { 512 <span class="hljs-comment">// Each line in the readline input will be successively available here as</span> 513 <span class="hljs-comment">// `line`.</span> 514 } 515}</code></pre> 516<p><code>readline.createInterface()</code> will start to consume the input stream once 517invoked. Having asynchronous operations between interface creation and 518asynchronous iteration may result in missed lines.</p> 519<h4><code>rl.line</code><span><a class="mark" href="#readline_rl_line" id="readline_rl_line">#</a></span></h4> 520<div class="api_metadata"> 521<details class="changelog"><summary>History</summary> 522<table> 523<tbody><tr><th>Version</th><th>Changes</th></tr> 524<tr><td>v14.18.0</td> 525<td><p>Value will always be a string, never undefined.</p></td></tr> 526<tr><td>v0.1.98</td> 527<td><p><span>Added in: v0.1.98</span></p></td></tr> 528</tbody></table> 529</details> 530</div> 531<ul> 532<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 533</ul> 534<p>The current input data being processed by node.</p> 535<p>This can be used when collecting input from a TTY stream to retrieve the 536current value that has been processed thus far, prior to the <code>line</code> event 537being emitted. Once the <code>line</code> event has been emitted, this property will 538be an empty string.</p> 539<p>Be aware that modifying the value during the instance runtime may have 540unintended consequences if <code>rl.cursor</code> is not also controlled.</p> 541<p><strong>If not using a TTY stream for input, use the <a href="#readline_event_line"><code>'line'</code></a> event.</strong></p> 542<p>One possible use case would be as follows:</p> 543<pre><code class="language-js"><span class="hljs-keyword">const</span> values = [<span class="hljs-string">'lorem ipsum'</span>, <span class="hljs-string">'dolor sit amet'</span>]; 544<span class="hljs-keyword">const</span> rl = readline.<span class="hljs-title function_">createInterface</span>(process.<span class="hljs-property">stdin</span>); 545<span class="hljs-keyword">const</span> showResults = <span class="hljs-title function_">debounce</span>(<span class="hljs-function">() =></span> { 546 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>( 547 <span class="hljs-string">'\n'</span>, 548 values.<span class="hljs-title function_">filter</span>(<span class="hljs-function">(<span class="hljs-params">val</span>) =></span> val.<span class="hljs-title function_">startsWith</span>(rl.<span class="hljs-property">line</span>)).<span class="hljs-title function_">join</span>(<span class="hljs-string">' '</span>) 549 ); 550}, <span class="hljs-number">300</span>); 551process.<span class="hljs-property">stdin</span>.<span class="hljs-title function_">on</span>(<span class="hljs-string">'keypress'</span>, <span class="hljs-function">(<span class="hljs-params">c, k</span>) =></span> { 552 <span class="hljs-title function_">showResults</span>(); 553});</code></pre> 554<h4><code>rl.cursor</code><span><a class="mark" href="#readline_rl_cursor" id="readline_rl_cursor">#</a></span></h4> 555<div class="api_metadata"> 556<span>Added in: v0.1.98</span> 557</div> 558<ul> 559<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a></li> 560</ul> 561<p>The cursor position relative to <code>rl.line</code>.</p> 562<p>This will track where the current cursor lands in the input string, when 563reading input from a TTY stream. The position of cursor determines the 564portion of the input string that will be modified as input is processed, 565as well as the column where the terminal caret will be rendered.</p> 566<h4><code>rl.getCursorPos()</code><span><a class="mark" href="#readline_rl_getcursorpos" id="readline_rl_getcursorpos">#</a></span></h4> 567<div class="api_metadata"> 568<span>Added in: v13.5.0, v12.16.0</span> 569</div> 570<ul> 571<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 572<ul> 573<li><code>rows</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> the row of the prompt the cursor currently lands on</li> 574<li><code>cols</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> the screen column the cursor currently lands on</li> 575</ul> 576</li> 577</ul> 578<p>Returns the real position of the cursor in relation to the input 579prompt + string. Long input (wrapping) strings, as well as multiple 580line prompts are included in the calculations.</p> 581</section><section><h3><code>readline.clearLine(stream, dir[, callback])</code><span><a class="mark" href="#readline_readline_clearline_stream_dir_callback" id="readline_readline_clearline_stream_dir_callback">#</a></span></h3> 582<div class="api_metadata"> 583<details class="changelog"><summary>History</summary> 584<table> 585<tbody><tr><th>Version</th><th>Changes</th></tr> 586<tr><td>v12.7.0</td> 587<td><p>The stream's write() callback and return value are exposed.</p></td></tr> 588<tr><td>v0.7.7</td> 589<td><p><span>Added in: v0.7.7</span></p></td></tr> 590</tbody></table> 591</details> 592</div> 593<ul> 594<li><code>stream</code> <a href="stream.html#stream_class_stream_writable" class="type"><stream.Writable></a></li> 595<li><code>dir</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> 596<ul> 597<li><code>-1</code>: to the left from cursor</li> 598<li><code>1</code>: to the right from cursor</li> 599<li><code>0</code>: the entire line</li> 600</ul> 601</li> 602<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Invoked once the operation completes.</li> 603<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>false</code> if <code>stream</code> wishes for the calling code to wait for 604the <code>'drain'</code> event to be emitted before continuing to write additional data; 605otherwise <code>true</code>.</li> 606</ul> 607<p>The <code>readline.clearLine()</code> method clears current line of given <a href="tty.html">TTY</a> stream 608in a specified direction identified by <code>dir</code>.</p> 609</section><section><h3><code>readline.clearScreenDown(stream[, callback])</code><span><a class="mark" href="#readline_readline_clearscreendown_stream_callback" id="readline_readline_clearscreendown_stream_callback">#</a></span></h3> 610<div class="api_metadata"> 611<details class="changelog"><summary>History</summary> 612<table> 613<tbody><tr><th>Version</th><th>Changes</th></tr> 614<tr><td>v12.7.0</td> 615<td><p>The stream's write() callback and return value are exposed.</p></td></tr> 616<tr><td>v0.7.7</td> 617<td><p><span>Added in: v0.7.7</span></p></td></tr> 618</tbody></table> 619</details> 620</div> 621<ul> 622<li><code>stream</code> <a href="stream.html#stream_class_stream_writable" class="type"><stream.Writable></a></li> 623<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Invoked once the operation completes.</li> 624<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>false</code> if <code>stream</code> wishes for the calling code to wait for 625the <code>'drain'</code> event to be emitted before continuing to write additional data; 626otherwise <code>true</code>.</li> 627</ul> 628<p>The <code>readline.clearScreenDown()</code> method clears the given <a href="tty.html">TTY</a> stream from 629the current position of the cursor down.</p> 630</section><section><h3><code>readline.createInterface(options)</code><span><a class="mark" href="#readline_readline_createinterface_options" id="readline_readline_createinterface_options">#</a></span></h3> 631<div class="api_metadata"> 632<details class="changelog"><summary>History</summary> 633<table> 634<tbody><tr><th>Version</th><th>Changes</th></tr> 635<tr><td>v14.18.0</td> 636<td><p>The <code>signal</code> option is supported now.</p></td></tr> 637<tr><td>v14.18.0</td> 638<td><p>The <code>history</code> option is supported now.</p></td></tr> 639<tr><td>v13.9.0</td> 640<td><p>The <code>tabSize</code> option is supported now.</p></td></tr> 641<tr><td>v8.3.0, v6.11.4</td> 642<td><p>Remove max limit of <code>crlfDelay</code> option.</p></td></tr> 643<tr><td>v6.6.0</td> 644<td><p>The <code>crlfDelay</code> option is supported now.</p></td></tr> 645<tr><td>v6.3.0</td> 646<td><p>The <code>prompt</code> option is supported now.</p></td></tr> 647<tr><td>v6.0.0</td> 648<td><p>The <code>historySize</code> option can be <code>0</code> now.</p></td></tr> 649<tr><td>v0.1.98</td> 650<td><p><span>Added in: v0.1.98</span></p></td></tr> 651</tbody></table> 652</details> 653</div> 654<ul> 655<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 656<ul> 657<li><code>input</code> <a href="stream.html#stream_class_stream_readable" class="type"><stream.Readable></a> The <a href="stream.html#stream_readable_streams">Readable</a> stream to listen to. This option 658is <em>required</em>.</li> 659<li><code>output</code> <a href="stream.html#stream_class_stream_writable" class="type"><stream.Writable></a> The <a href="stream.html#stream_writable_streams">Writable</a> stream to write readline data 660to.</li> 661<li><code>completer</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> An optional function used for Tab autocompletion.</li> 662<li><code>terminal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> if the <code>input</code> and <code>output</code> streams should be 663treated like a TTY, and have ANSI/VT100 escape codes written to it. 664<strong>Default:</strong> checking <code>isTTY</code> on the <code>output</code> stream upon instantiation.</li> 665<li><code>history</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a> Initial list of history lines. This option makes sense 666only if <code>terminal</code> is set to <code>true</code> by the user or by an internal <code>output</code> 667check, otherwise the history caching mechanism is not initialized at all. 668<strong>Default:</strong> <code>[]</code>.</li> 669<li><code>historySize</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> Maximum number of history lines retained. To disable 670the history set this value to <code>0</code>. This option makes sense only if 671<code>terminal</code> is set to <code>true</code> by the user or by an internal <code>output</code> check, 672otherwise the history caching mechanism is not initialized at all. 673<strong>Default:</strong> <code>30</code>.</li> 674<li><code>removeHistoryDuplicates</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>true</code>, when a new input line added 675to the history list duplicates an older one, this removes the older line 676from the list. <strong>Default:</strong> <code>false</code>.</li> 677<li><code>prompt</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The prompt string to use. <strong>Default:</strong> <code>'> '</code>.</li> 678<li><code>crlfDelay</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> If the delay between <code>\r</code> and <code>\n</code> exceeds 679<code>crlfDelay</code> milliseconds, both <code>\r</code> and <code>\n</code> will be treated as separate 680end-of-line input. <code>crlfDelay</code> will be coerced to a number no less than 681<code>100</code>. It can be set to <code>Infinity</code>, in which case <code>\r</code> followed by <code>\n</code> 682will always be considered a single newline (which may be reasonable for 683<a href="#readline_example_read_file_stream_line_by_line">reading files</a> with <code>\r\n</code> line delimiter). <strong>Default:</strong> <code>100</code>.</li> 684<li><code>escapeCodeTimeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The duration <code>readline</code> will wait for a 685character (when reading an ambiguous key sequence in milliseconds one that 686can both form a complete key sequence using the input read so far and can 687take additional input to complete a longer key sequence). 688<strong>Default:</strong> <code>500</code>.</li> 689<li><code>tabSize</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> The number of spaces a tab is equal to (minimum 1). 690<strong>Default:</strong> <code>8</code>.</li> 691<li><code>signal</code> <a href="globals.html#globals_class_abortsignal" class="type"><AbortSignal></a> Allows closing the interface using an AbortSignal. 692Aborting the signal will internally call <code>close</code> on the interface.</li> 693</ul> 694</li> 695<li>Returns: <a href="readline.html#readline_class_interface" class="type"><readline.Interface></a></li> 696</ul> 697<p>The <code>readline.createInterface()</code> method creates a new <code>readline.Interface</code> 698instance.</p> 699<pre><code class="language-js"><span class="hljs-keyword">const</span> readline = <span class="hljs-built_in">require</span>(<span class="hljs-string">'readline'</span>); 700<span class="hljs-keyword">const</span> rl = readline.<span class="hljs-title function_">createInterface</span>({ 701 <span class="hljs-attr">input</span>: process.<span class="hljs-property">stdin</span>, 702 <span class="hljs-attr">output</span>: process.<span class="hljs-property">stdout</span> 703});</code></pre> 704<p>Once the <code>readline.Interface</code> instance is created, the most common case is to 705listen for the <code>'line'</code> event:</p> 706<pre><code class="language-js">rl.<span class="hljs-title function_">on</span>(<span class="hljs-string">'line'</span>, <span class="hljs-function">(<span class="hljs-params">line</span>) =></span> { 707 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Received: <span class="hljs-subst">${line}</span>`</span>); 708});</code></pre> 709<p>If <code>terminal</code> is <code>true</code> for this instance then the <code>output</code> stream will get 710the best compatibility if it defines an <code>output.columns</code> property and emits 711a <code>'resize'</code> event on the <code>output</code> if or when the columns ever change 712(<a href="process.html#process_process_stdout"><code>process.stdout</code></a> does this automatically when it is a TTY).</p> 713<p>When creating a <code>readline.Interface</code> using <code>stdin</code> as input, the program 714will not terminate until it receives <code>EOF</code> (<kbd>Ctrl</kbd>+<kbd>D</kbd> on 715Linux/macOS, <kbd>Ctrl</kbd>+<kbd>Z</kbd> followed by <kbd>Return</kbd> on 716Windows). 717If you want your application to exit without waiting for user input, you can 718<a href="net.html#net_socket_unref"><code>unref()</code></a> the standard input stream:</p> 719<pre><code class="language-js">process.<span class="hljs-property">stdin</span>.<span class="hljs-title function_">unref</span>();</code></pre> 720<h4>Use of the <code>completer</code> function<span><a class="mark" href="#readline_use_of_the_completer_function" id="readline_use_of_the_completer_function">#</a></span></h4> 721<p>The <code>completer</code> function takes the current line entered by the user 722as an argument, and returns an <code>Array</code> with 2 entries:</p> 723<ul> 724<li>An <code>Array</code> with matching entries for the completion.</li> 725<li>The substring that was used for the matching.</li> 726</ul> 727<p>For instance: <code>[[substr1, substr2, ...], originalsubstring]</code>.</p> 728<pre><code class="language-js"><span class="hljs-keyword">function</span> <span class="hljs-title function_">completer</span>(<span class="hljs-params">line</span>) { 729 <span class="hljs-keyword">const</span> completions = <span class="hljs-string">'.help .error .exit .quit .q'</span>.<span class="hljs-title function_">split</span>(<span class="hljs-string">' '</span>); 730 <span class="hljs-keyword">const</span> hits = completions.<span class="hljs-title function_">filter</span>(<span class="hljs-function">(<span class="hljs-params">c</span>) =></span> c.<span class="hljs-title function_">startsWith</span>(line)); 731 <span class="hljs-comment">// Show all completions if none found</span> 732 <span class="hljs-keyword">return</span> [hits.<span class="hljs-property">length</span> ? hits : completions, line]; 733}</code></pre> 734<p>The <code>completer</code> function can be called asynchronously if it accepts two 735arguments:</p> 736<pre><code class="language-js"><span class="hljs-keyword">function</span> <span class="hljs-title function_">completer</span>(<span class="hljs-params">linePartial, callback</span>) { 737 <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, [[<span class="hljs-string">'123'</span>], linePartial]); 738}</code></pre> 739</section><section><h3><code>readline.cursorTo(stream, x[, y][, callback])</code><span><a class="mark" href="#readline_readline_cursorto_stream_x_y_callback" id="readline_readline_cursorto_stream_x_y_callback">#</a></span></h3> 740<div class="api_metadata"> 741<details class="changelog"><summary>History</summary> 742<table> 743<tbody><tr><th>Version</th><th>Changes</th></tr> 744<tr><td>v12.7.0</td> 745<td><p>The stream's write() callback and return value are exposed.</p></td></tr> 746<tr><td>v0.7.7</td> 747<td><p><span>Added in: v0.7.7</span></p></td></tr> 748</tbody></table> 749</details> 750</div> 751<ul> 752<li><code>stream</code> <a href="stream.html#stream_class_stream_writable" class="type"><stream.Writable></a></li> 753<li><code>x</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 754<li><code>y</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 755<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Invoked once the operation completes.</li> 756<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>false</code> if <code>stream</code> wishes for the calling code to wait for 757the <code>'drain'</code> event to be emitted before continuing to write additional data; 758otherwise <code>true</code>.</li> 759</ul> 760<p>The <code>readline.cursorTo()</code> method moves cursor to the specified position in a 761given <a href="tty.html">TTY</a> <code>stream</code>.</p> 762</section><section><h3><code>readline.emitKeypressEvents(stream[, interface])</code><span><a class="mark" href="#readline_readline_emitkeypressevents_stream_interface" id="readline_readline_emitkeypressevents_stream_interface">#</a></span></h3> 763<div class="api_metadata"> 764<span>Added in: v0.7.7</span> 765</div> 766<ul> 767<li><code>stream</code> <a href="stream.html#stream_class_stream_readable" class="type"><stream.Readable></a></li> 768<li><code>interface</code> <a href="readline.html#readline_class_interface" class="type"><readline.Interface></a></li> 769</ul> 770<p>The <code>readline.emitKeypressEvents()</code> method causes the given <a href="stream.html#stream_readable_streams">Readable</a> 771stream to begin emitting <code>'keypress'</code> events corresponding to received input.</p> 772<p>Optionally, <code>interface</code> specifies a <code>readline.Interface</code> instance for which 773autocompletion is disabled when copy-pasted input is detected.</p> 774<p>If the <code>stream</code> is a <a href="tty.html">TTY</a>, then it must be in raw mode.</p> 775<p>This is automatically called by any readline instance on its <code>input</code> if the 776<code>input</code> is a terminal. Closing the <code>readline</code> instance does not stop 777the <code>input</code> from emitting <code>'keypress'</code> events.</p> 778<pre><code class="language-js">readline.<span class="hljs-title function_">emitKeypressEvents</span>(process.<span class="hljs-property">stdin</span>); 779<span class="hljs-keyword">if</span> (process.<span class="hljs-property">stdin</span>.<span class="hljs-property">isTTY</span>) 780 process.<span class="hljs-property">stdin</span>.<span class="hljs-title function_">setRawMode</span>(<span class="hljs-literal">true</span>);</code></pre> 781</section><section><h3><code>readline.moveCursor(stream, dx, dy[, callback])</code><span><a class="mark" href="#readline_readline_movecursor_stream_dx_dy_callback" id="readline_readline_movecursor_stream_dx_dy_callback">#</a></span></h3> 782<div class="api_metadata"> 783<details class="changelog"><summary>History</summary> 784<table> 785<tbody><tr><th>Version</th><th>Changes</th></tr> 786<tr><td>v12.7.0</td> 787<td><p>The stream's write() callback and return value are exposed.</p></td></tr> 788<tr><td>v0.7.7</td> 789<td><p><span>Added in: v0.7.7</span></p></td></tr> 790</tbody></table> 791</details> 792</div> 793<ul> 794<li><code>stream</code> <a href="stream.html#stream_class_stream_writable" class="type"><stream.Writable></a></li> 795<li><code>dx</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 796<li><code>dy</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 797<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Invoked once the operation completes.</li> 798<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>false</code> if <code>stream</code> wishes for the calling code to wait for 799the <code>'drain'</code> event to be emitted before continuing to write additional data; 800otherwise <code>true</code>.</li> 801</ul> 802<p>The <code>readline.moveCursor()</code> method moves the cursor <em>relative</em> to its current 803position in a given <a href="tty.html">TTY</a> <code>stream</code>.</p> 804</section><section><h3>Example: Tiny CLI<span><a class="mark" href="#readline_example_tiny_cli" id="readline_example_tiny_cli">#</a></span></h3> 805<p>The following example illustrates the use of <code>readline.Interface</code> class to 806implement a small command-line interface:</p> 807<pre><code class="language-js"><span class="hljs-keyword">const</span> readline = <span class="hljs-built_in">require</span>(<span class="hljs-string">'readline'</span>); 808<span class="hljs-keyword">const</span> rl = readline.<span class="hljs-title function_">createInterface</span>({ 809 <span class="hljs-attr">input</span>: process.<span class="hljs-property">stdin</span>, 810 <span class="hljs-attr">output</span>: process.<span class="hljs-property">stdout</span>, 811 <span class="hljs-attr">prompt</span>: <span class="hljs-string">'OHAI> '</span> 812}); 813 814rl.<span class="hljs-title function_">prompt</span>(); 815 816rl.<span class="hljs-title function_">on</span>(<span class="hljs-string">'line'</span>, <span class="hljs-function">(<span class="hljs-params">line</span>) =></span> { 817 <span class="hljs-keyword">switch</span> (line.<span class="hljs-title function_">trim</span>()) { 818 <span class="hljs-keyword">case</span> <span class="hljs-string">'hello'</span>: 819 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'world!'</span>); 820 <span class="hljs-keyword">break</span>; 821 <span class="hljs-attr">default</span>: 822 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Say what? I might have heard '<span class="hljs-subst">${line.trim()}</span>'`</span>); 823 <span class="hljs-keyword">break</span>; 824 } 825 rl.<span class="hljs-title function_">prompt</span>(); 826}).<span class="hljs-title function_">on</span>(<span class="hljs-string">'close'</span>, <span class="hljs-function">() =></span> { 827 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'Have a great day!'</span>); 828 process.<span class="hljs-title function_">exit</span>(<span class="hljs-number">0</span>); 829});</code></pre> 830</section><section><h3>Example: Read file stream line-by-Line<span><a class="mark" href="#readline_example_read_file_stream_line_by_line" id="readline_example_read_file_stream_line_by_line">#</a></span></h3> 831<p>A common use case for <code>readline</code> is to consume an input file one line at a 832time. The easiest way to do so is leveraging the <a href="fs.html#fs_class_fs_readstream"><code>fs.ReadStream</code></a> API as 833well as a <code>for await...of</code> loop:</p> 834<pre><code class="language-js"><span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'fs'</span>); 835<span class="hljs-keyword">const</span> readline = <span class="hljs-built_in">require</span>(<span class="hljs-string">'readline'</span>); 836 837<span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">processLineByLine</span>(<span class="hljs-params"></span>) { 838 <span class="hljs-keyword">const</span> fileStream = fs.<span class="hljs-title function_">createReadStream</span>(<span class="hljs-string">'input.txt'</span>); 839 840 <span class="hljs-keyword">const</span> rl = readline.<span class="hljs-title function_">createInterface</span>({ 841 <span class="hljs-attr">input</span>: fileStream, 842 <span class="hljs-attr">crlfDelay</span>: <span class="hljs-title class_">Infinity</span> 843 }); 844 <span class="hljs-comment">// Note: we use the crlfDelay option to recognize all instances of CR LF</span> 845 <span class="hljs-comment">// ('\r\n') in input.txt as a single line break.</span> 846 847 <span class="hljs-keyword">for</span> <span class="hljs-keyword">await</span> (<span class="hljs-keyword">const</span> line <span class="hljs-keyword">of</span> rl) { 848 <span class="hljs-comment">// Each line in input.txt will be successively available here as `line`.</span> 849 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Line from file: <span class="hljs-subst">${line}</span>`</span>); 850 } 851} 852 853<span class="hljs-title function_">processLineByLine</span>();</code></pre> 854<p>Alternatively, one could use the <a href="#readline_event_line"><code>'line'</code></a> event:</p> 855<pre><code class="language-js"><span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'fs'</span>); 856<span class="hljs-keyword">const</span> readline = <span class="hljs-built_in">require</span>(<span class="hljs-string">'readline'</span>); 857 858<span class="hljs-keyword">const</span> rl = readline.<span class="hljs-title function_">createInterface</span>({ 859 <span class="hljs-attr">input</span>: fs.<span class="hljs-title function_">createReadStream</span>(<span class="hljs-string">'sample.txt'</span>), 860 <span class="hljs-attr">crlfDelay</span>: <span class="hljs-title class_">Infinity</span> 861}); 862 863rl.<span class="hljs-title function_">on</span>(<span class="hljs-string">'line'</span>, <span class="hljs-function">(<span class="hljs-params">line</span>) =></span> { 864 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Line from file: <span class="hljs-subst">${line}</span>`</span>); 865});</code></pre> 866<p>Currently, <code>for await...of</code> loop can be a bit slower. If <code>async</code> / <code>await</code> 867flow and speed are both essential, a mixed approach can be applied:</p> 868<pre><code class="language-js"><span class="hljs-keyword">const</span> { once } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'events'</span>); 869<span class="hljs-keyword">const</span> { createReadStream } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'fs'</span>); 870<span class="hljs-keyword">const</span> { createInterface } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'readline'</span>); 871 872(<span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">processLineByLine</span>(<span class="hljs-params"></span>) { 873 <span class="hljs-keyword">try</span> { 874 <span class="hljs-keyword">const</span> rl = <span class="hljs-title function_">createInterface</span>({ 875 <span class="hljs-attr">input</span>: <span class="hljs-title function_">createReadStream</span>(<span class="hljs-string">'big-file.txt'</span>), 876 <span class="hljs-attr">crlfDelay</span>: <span class="hljs-title class_">Infinity</span> 877 }); 878 879 rl.<span class="hljs-title function_">on</span>(<span class="hljs-string">'line'</span>, <span class="hljs-function">(<span class="hljs-params">line</span>) =></span> { 880 <span class="hljs-comment">// Process the line.</span> 881 }); 882 883 <span class="hljs-keyword">await</span> <span class="hljs-title function_">once</span>(rl, <span class="hljs-string">'close'</span>); 884 885 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'File processed.'</span>); 886 } <span class="hljs-keyword">catch</span> (err) { 887 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">error</span>(err); 888 } 889})();</code></pre> 890</section><section><h3>TTY keybindings<span><a class="mark" href="#readline_tty_keybindings" id="readline_tty_keybindings">#</a></span></h3> 891<table> 892 <tbody><tr> 893 <th>Keybindings</th> 894 <th>Description</th> 895 <th>Notes</th> 896 </tr> 897 <tr> 898 <td><kbd>Ctrl</kbd>+<kbd>Shift</kbd>+<kbd>Backspace</kbd></td> 899 <td>Delete line left</td> 900 <td>Doesn't work on Linux, Mac and Windows</td> 901 </tr> 902 <tr> 903 <td><kbd>Ctrl</kbd>+<kbd>Shift</kbd>+<kbd>Delete</kbd></td> 904 <td>Delete line right</td> 905 <td>Doesn't work on Mac</td> 906 </tr> 907 <tr> 908 <td><kbd>Ctrl</kbd>+<kbd>C</kbd></td> 909 <td>Emit <code>SIGINT</code> or close the readline instance</td> 910 <td></td> 911 </tr> 912 <tr> 913 <td><kbd>Ctrl</kbd>+<kbd>H</kbd></td> 914 <td>Delete left</td> 915 <td></td> 916 </tr> 917 <tr> 918 <td><kbd>Ctrl</kbd>+<kbd>D</kbd></td> 919 <td>Delete right or close the readline instance in case the current line is empty / EOF</td> 920 <td>Doesn't work on Windows</td> 921 </tr> 922 <tr> 923 <td><kbd>Ctrl</kbd>+<kbd>U</kbd></td> 924 <td>Delete from the current position to the line start</td> 925 <td></td> 926 </tr> 927 <tr> 928 <td><kbd>Ctrl</kbd>+<kbd>K</kbd></td> 929 <td>Delete from the current position to the end of line</td> 930 <td></td> 931 </tr> 932 <tr> 933 <td><kbd>Ctrl</kbd>+<kbd>A</kbd></td> 934 <td>Go to start of line</td> 935 <td></td> 936 </tr> 937 <tr> 938 <td><kbd>Ctrl</kbd>+<kbd>E</kbd></td> 939 <td>Go to to end of line</td> 940 <td></td> 941 </tr> 942 <tr> 943 <td><kbd>Ctrl</kbd>+<kbd>B</kbd></td> 944 <td>Back one character</td> 945 <td></td> 946 </tr> 947 <tr> 948 <td><kbd>Ctrl</kbd>+<kbd>F</kbd></td> 949 <td>Forward one character</td> 950 <td></td> 951 </tr> 952 <tr> 953 <td><kbd>Ctrl</kbd>+<kbd>L</kbd></td> 954 <td>Clear screen</td> 955 <td></td> 956 </tr> 957 <tr> 958 <td><kbd>Ctrl</kbd>+<kbd>N</kbd></td> 959 <td>Next history item</td> 960 <td></td> 961 </tr> 962 <tr> 963 <td><kbd>Ctrl</kbd>+<kbd>P</kbd></td> 964 <td>Previous history item</td> 965 <td></td> 966 </tr> 967 <tr> 968 <td><kbd>Ctrl</kbd>+<kbd>Z</kbd></td> 969 <td>Moves running process into background. Type 970 <code>fg</code> and press <kbd>Enter</kbd> 971 to return.</td> 972 <td>Doesn't work on Windows</td> 973 </tr> 974 <tr> 975 <td><kbd>Ctrl</kbd>+<kbd>W</kbd> or <kbd>Ctrl</kbd> 976 +<kbd>Backspace</kbd></td> 977 <td>Delete backward to a word boundary</td> 978 <td><kbd>Ctrl</kbd>+<kbd>Backspace</kbd> Doesn't 979 work on Linux, Mac and Windows</td> 980 </tr> 981 <tr> 982 <td><kbd>Ctrl</kbd>+<kbd>Delete</kbd></td> 983 <td>Delete forward to a word boundary</td> 984 <td>Doesn't work on Mac</td> 985 </tr> 986 <tr> 987 <td><kbd>Ctrl</kbd>+<kbd>Left arrow</kbd> or 988 <kbd>Meta</kbd>+<kbd>B</kbd></td> 989 <td>Word left</td> 990 <td><kbd>Ctrl</kbd>+<kbd>Left arrow</kbd> Doesn't work 991 on Mac</td> 992 </tr> 993 <tr> 994 <td><kbd>Ctrl</kbd>+<kbd>Right arrow</kbd> or 995 <kbd>Meta</kbd>+<kbd>F</kbd></td> 996 <td>Word right</td> 997 <td><kbd>Ctrl</kbd>+<kbd>Right arrow</kbd> Doesn't work 998 on Mac</td> 999 </tr> 1000 <tr> 1001 <td><kbd>Meta</kbd>+<kbd>D</kbd> or <kbd>Meta</kbd> 1002 +<kbd>Delete</kbd></td> 1003 <td>Delete word right</td> 1004 <td><kbd>Meta</kbd>+<kbd>Delete</kbd> Doesn't work 1005 on windows</td> 1006 </tr> 1007 <tr> 1008 <td><kbd>Meta</kbd>+<kbd>Backspace</kbd></td> 1009 <td>Delete word left</td> 1010 <td>Doesn't work on Mac</td> 1011 </tr> 1012</tbody></table></section> 1013 <!-- API END --> 1014 </div> 1015 </div> 1016 </div> 1017 <script> 1018 'use strict'; 1019 { 1020 const kCustomPreference = 'customDarkTheme'; 1021 const userSettings = sessionStorage.getItem(kCustomPreference); 1022 const themeToggleButton = document.getElementById('theme-toggle-btn'); 1023 if (userSettings === null && window.matchMedia) { 1024 const mq = window.matchMedia('(prefers-color-scheme: dark)'); 1025 if ('onchange' in mq) { 1026 function mqChangeListener(e) { 1027 document.body.classList.toggle('dark-mode', e.matches); 1028 } 1029 mq.addEventListener('change', mqChangeListener); 1030 if (themeToggleButton) { 1031 themeToggleButton.addEventListener('click', function() { 1032 mq.removeEventListener('change', mqChangeListener); 1033 }, { once: true }); 1034 } 1035 } 1036 if (mq.matches) { 1037 document.body.classList.add('dark-mode'); 1038 } 1039 } else if (userSettings === 'true') { 1040 document.body.classList.add('dark-mode'); 1041 } 1042 if (themeToggleButton) { 1043 themeToggleButton.hidden = false; 1044 themeToggleButton.addEventListener('click', function() { 1045 sessionStorage.setItem( 1046 kCustomPreference, 1047 document.body.classList.toggle('dark-mode') 1048 ); 1049 }); 1050 } 1051 } 1052 </script> 1053</body> 1054</html> 1055