1# @ohos.hilog (HiLog) 2 3The HiLog subsystem allows your applications or services to output logs based on the specified type, level, and format string. Such logs help you learn the running status of applications and better debug programs. 4 5> **NOTE** 6> 7> The initial APIs of this module are supported since API version 7. Newly added APIs will be marked with a superscript to indicate their earliest API version. 8 9## Modules to Import 10 11```js 12import hilog from '@ohos.hilog'; 13``` 14 15## hilog.isLoggable 16 17isLoggable(domain: number, tag: string, level: LogLevel) : boolean 18 19Checks whether logs are printable based on the specified service domain, log tag, and log level. 20 21**System capability**: SystemCapability.HiviewDFX.HiLog 22 23**Parameters** 24 25| Name| Type | Mandatory| Description | 26| ------ | --------------------- | ---- | ------------------------------------------------------------ | 27| domain | number | Yes | Service domain of logs. The value ranges from **0x0** to **0xFFFF**.<br>You can define the value as required.| 28| tag | string | Yes | Log tag in the string format. You are advised to use this parameter to identify a particular service behavior or the class holding the ongoing method.| 29| level | [LogLevel](#loglevel) | Yes | Log level. | 30 31**Return value** 32 33| Type | Description | 34| ------- | ------------------------------------------------------------ | 35| boolean | Returns **true** logs are printable based on the specified service domain, log tag, and log level; returns **false** otherwise.| 36 37**Example** 38 39```js 40hilog.isLoggable(0x0001, "testTag", hilog.LogLevel.INFO); 41``` 42 43## LogLevel 44 45Log level. 46 47**System capability**: SystemCapability.HiviewDFX.HiLog 48 49| Name | Value | Description | 50| ----- | ------ | ------------------------------------------------------------ | 51| DEBUG | 3 | Log level used to record more detailed process information than INFO logs to help developers analyze service processes and locate faults.| 52| INFO | 4 | Log level used to record key service process nodes and exceptions that occur during service running,<br>for example, no network signal or login failure.<br>These logs should be recorded by the dominant module in the service to avoid repeated logging conducted by multiple invoked modules or low-level functions.| 53| WARN | 5 | Log level used to record severe, unexpected faults that have little impact on users and can be rectified by the programs themselves or through simple operations.| 54| ERROR | 6 | Log level used to record program or functional errors that affect the normal running or use of the functionality and can be fixed at a high cost, for example, by resetting data.| 55| FATAL | 7 | Log level used to record program or functionality crashes that cannot be rectified. | 56 57## hilog.debug 58 59debug(domain: number, tag: string, format: string, ...args: any[]) : void 60 61Prints DEBUG logs. 62 63DEBUG logs are not recorded in official versions by default. They are available in debug versions or in official versions with the debug function enabled. 64 65**System capability**: SystemCapability.HiviewDFX.HiLog 66 67**Parameters** 68 69| Name| Type | Mandatory| Description | 70| ------ | ------ | ---- | ------------------------------------------------------------ | 71| domain | number | Yes | Service domain of logs. The value ranges from **0x0** to **0xFFFF**.<br>You can define the value as required.| 72| tag | string | Yes | Log tag in the string format. You are advised to use this parameter to identify a particular service behavior or the class holding the ongoing method.| 73| format | string | Yes | Format string used to output logs in a specified format. It can contain several elements, where the parameter type and privacy identifier are mandatory.<br>Parameters labeled **{public}** are public data and are displayed in plaintext; parameters labeled **{private}** (default value) are private data and are filtered by **\<private>**.| 74| args | any[] | Yes | Variable-length parameter list corresponding to the format string. The number and type of parameters must map to the identifier in the format string.| 75 76**Example** 77 78This example is used to output a DEBUG log with the format string being `"%{public}s World %{private}d"`. The variable `%{public}s` is a plaintext string, and the variable `%{private}d` is a private integer. 79 80```js 81hilog.debug(0x0001, "testTag", "%{public}s World %{private}d", "hello", 3); 82``` 83 84If `"hello"` is filled in `%{public}s` and `3` in `%{private}d`, the output log is as follows: 85 86``` 8708-05 12:21:47.579 2695-2703/com.example.myapplication D 00001/testTag: hello World <private> 88``` 89 90## hilog.info 91 92info(domain: number, tag: string, format: string, ...args: any[]) : void 93 94Prints INFO logs. 95 96**System capability**: SystemCapability.HiviewDFX.HiLog 97 98**Parameters** 99 100| Name| Type | Mandatory| Description | 101| ------ | ------ | ---- | ------------------------------------------------------------ | 102| domain | number | Yes | Service domain of logs. The value ranges from **0x0** to **0xFFFF**.<br>You can define the value as required. | 103| tag | string | Yes | Log tag in the string format. You are advised to use this parameter to identify a particular service behavior or the class holding the ongoing method.| 104| format | string | Yes | Format string used to output logs in a specified format. It can contain several elements, where the parameter type and privacy identifier are mandatory.<br>Parameters labeled **{public}** are public data and are displayed in plaintext; parameters labeled **{private}** (default value) are private data and are filtered by **\<private>**.| 105| args | any[] | Yes | Variable-length parameter list corresponding to the format string. The number and type of parameters must map to the identifier in the format string.| 106 107**Example** 108 109This example is used to output an INFO log with the format string being `"%{public}s World %{private}d"`. The variable `%{public}s` is a plaintext string, and the variable `%{private}d` is a private integer. 110 111```js 112hilog.info(0x0001, "testTag", "%{public}s World %{private}d", "hello", 3); 113``` 114 115If `"hello"` is filled in `%{public}s` and `3` in `%{private}d`, the output log is as follows: 116 117``` 11808-05 12:21:47.579 2695-2703/com.example.myapplication I 00001/testTag: hello World <private> 119``` 120 121## hilog.warn 122 123warn(domain: number, tag: string, format: string, ...args: any[]) : void 124 125Prints WARN logs. 126 127**System capability**: SystemCapability.HiviewDFX.HiLog 128 129**Parameters** 130 131| Name| Type | Mandatory| Description | 132| ------ | ------ | ---- | ------------------------------------------------------------ | 133| domain | number | Yes | Service domain of logs. The value ranges from **0x0** to **0xFFFF**.<br>You can define the value as required. | 134| tag | string | Yes | Log tag in the string format. You are advised to use this parameter to identify a particular service behavior or the class holding the ongoing method.| 135| format | string | Yes | Format string used to output logs in a specified format. It can contain several elements, where the parameter type and privacy identifier are mandatory.<br>Parameters labeled **{public}** are public data and are displayed in plaintext; parameters labeled **{private}** (default value) are private data and are filtered by **\<private>**.| 136| args | any[] | Yes | Variable-length parameter list corresponding to the format string. The number and type of parameters must map to the identifier in the format string.| 137 138**Example** 139 140This example is used to output a WARN log with the format string being `"%{public}s World %{private}d"`. The variable `%{public}s` is a plaintext string, and the variable `%{private}d` is a private integer. 141 142```js 143hilog.warn(0x0001, "testTag", "%{public}s World %{private}d", "hello", 3); 144``` 145 146If `"hello"` is filled in `%{public}s` and `3` in `%{private}d`, the output log is as follows: 147 148``` 14908-05 12:21:47.579 2695-2703/com.example.myapplication W 00001/testTag: hello World <private> 150``` 151 152## hilog.error 153 154error(domain: number, tag: string, format: string, ...args: any[]) : void 155 156Prints ERROR logs. 157 158**System capability**: SystemCapability.HiviewDFX.HiLog 159 160**Parameters** 161 162| Name| Type | Mandatory| Description | 163| ------ | ------ | ---- | ------------------------------------------------------------ | 164| domain | number | Yes | Service domain of logs. The value ranges from **0x0** to **0xFFFF**.<br>You can define the value as required. | 165| tag | string | Yes | Log tag in the string format. You are advised to use this parameter to identify a particular service behavior or the class holding the ongoing method.| 166| format | string | Yes | Format string used to output logs in a specified format. It can contain several elements, where the parameter type and privacy identifier are mandatory.<br>Parameters labeled **{public}** are public data and are displayed in plaintext; parameters labeled **{private}** (default value) are private data and are filtered by **\<private>**.| 167| args | any[] | Yes | Variable-length parameter list corresponding to the format string. The number and type of parameters must map to the identifier in the format string.| 168 169**Example** 170 171This example is used to output an ERROR log with the format string being `"%{public}s World %{private}d"`. The variable `%{public}s` is a plaintext string, and the variable `%{private}d` is a private integer. 172 173```js 174hilog.error(0x0001, "testTag", "%{public}s World %{private}d", "hello", 3); 175``` 176 177If `"hello"` is filled in `%{public}s` and `3` in `%{private}d`, the output log is as follows: 178 179``` 18008-05 12:21:47.579 2695-2703/com.example.myapplication E 00001/testTag: hello World <private> 181``` 182 183## hilog.fatal 184 185fatal(domain: number, tag: string, format: string, ...args: any[]) : void 186 187Prints FATAL logs. 188 189**System capability**: SystemCapability.HiviewDFX.HiLog 190 191**Parameters** 192 193| Name| Type | Mandatory| Description | 194| ------ | ------ | ---- | ------------------------------------------------------------ | 195| domain | number | Yes | Service domain of logs. The value ranges from **0x0** to **0xFFFF**.<br>You can define the value as required. | 196| tag | string | Yes | Log tag in the string format. You are advised to use this parameter to identify a particular service behavior or the class holding the ongoing method.| 197| format | string | Yes | Format string used to output logs in a specified format. It can contain several elements, where the parameter type and privacy identifier are mandatory.<br>Parameters labeled **{public}** are public data and are displayed in plaintext; parameters labeled **{private}** (default value) are private data and are filtered by **\<private>**.| 198| args | any[] | Yes | Variable-length parameter list corresponding to the format string. The number and type of parameters must map to the identifier in the format string.| 199 200**Example** 201 202This example is used to output a FATAL log with the format string being `"%{public}s World %{private}d"`. The variable `%{public}s` is a plaintext string, and the variable `%{private}d` is a private integer. 203 204```js 205hilog.fatal(0x0001, "testTag", "%{public}s World %{private}d", "hello", 3); 206``` 207 208If `"hello"` is filled in `%{public}s` and `3` in `%{private}d`, the output log is as follows: 209 210``` 21108-05 12:21:47.579 2695-2703/com.example.myapplication F 00001/testTag: hello World <private> 212``` 213 214## Parameter Format 215 216Parameters in the log are printed in the following format: 217 218%{[private flag]}specifier 219 220| Privacy Flag| Description| 221| ------------ | ---- | 222| Unspecified | The default value is **private**, indicating that parameters in plaintext are not printed.| 223| private | Prints private parameters.| 224| public | Prints parameters in plaintext.| 225 226| Specifier| Description| Example| 227| ------------ | ---- | ---- | 228| d/i | Prints logs of the **number** and **bigint** types.| 123 | 229| s | Prints logs of the **string undefined bool** and **null** types.| "123" | 230 231**Example** 232```js 233let testObj: Record<string, string | number> = { 234 'name': "Jack", 235 'age': 22 236} 237let isBol = true; 238let bigNum = BigInt(1234567890123456789); 239hilog.info(0x0001, "jsHilogTest", "print object: %{public}s", JSON.stringify(testObj)); 240hilog.info(0x0001, "jsHilogTest", "private flag: %{private}s %s, print null: %{public}s", "hello", "world", null); 241hilog.info(0x0001, "jsHilogTest", "print undefined: %{public}s", undefined); 242hilog.info(0x0001, "jsHilogTest", "print number: %{public}d %{public}i", 123, 456); 243hilog.info(0x0001, "jsHilogTest", "print bigNum: %{public}d %{public}i", bigNum, bigNum); 244hilog.info(0x0001, "jsHilogTest", "print boolean: %{public}s", isBol); 245``` 246 247Log printing result: 248``` 24908-09 13:26:29.094 2266 2266 I A00001/jsHilogTest: print object: {"name":"Jack","age":22} 25008-09 13:26:29.094 2266 2266 I A00001/jsHilogTest: private flag: <private> <private>, print null: null 25108-09 13:26:29.094 2266 2266 I A00001/jsHilogTest: print undefined: undefined 25208-09 13:26:29.094 2266 2266 I A00001/jsHilogTest: print number: 123 456 25308-09 13:26:29.095 2266 2266 I A00001/jsHilogTest: print bigNum: 1234567890123456768 1234567890123456768 25408-09 13:26:29.095 2266 2266 I A00001/jsHilogTest: print boolean: true 255``` 256