1# @ohos.hilog (HiLog) 2 3The **hilog** module 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**<br> 6> 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. 7 8## Modules to Import 9 10```js 11import hilog from '@ohos.hilog'; 12``` 13 14## hilog.isLoggable 15 16isLoggable(domain: number, tag: string, level: LogLevel) : boolean 17 18Checks whether logs are printable based on the specified service domain, log tag, and log level. 19 20**System capability**: SystemCapability.HiviewDFX.HiLog 21 22**Parameters** 23 24| Name| Type | Mandatory| Description | 25| ------ | --------------------- | ---- | ------------------------------------------------------------ | 26| domain | number | Yes | Service domain of logs. The value ranges from **0x0** to **0xFFFF**. You can define the value within your application as required.| 27| 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.| 28| level | [LogLevel](#loglevel) | Yes | Log level. | 29 30**Return value** 31 32| Type | Description | 33| ------- | ------------------------------------------------------------ | 34| boolean | Returns **true** logs are printable based on the specified service domain, log tag, and log level; returns **false** otherwise.| 35 36**Example** 37 38```js 39hilog.isLoggable(0x0001, "testTag", hilog.LogLevel.INFO); 40``` 41 42## LogLevel 43 44Enumerates the log levels. 45 46**System capability**: SystemCapability.HiviewDFX.HiLog 47 48| Name | Value| Description | 49| ----- | ------ | ------------------------------------------------------------ | 50| DEBUG | 3 | Log level used to record more detailed process information than INFO logs to help developers analyze service processes and locate faults.| 51| 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.| 52| 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.| 53| 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.| 54| FATAL | 7 | Log level used to record program or functionality crashes that cannot be rectified. | 55 56## hilog.debug 57 58debug(domain: number, tag: string, format: string, ...args: any[]) : void 59 60Prints DEBUG logs. 61 62DEBUG logs are not recorded in official versions by default. They are available in debug versions or in official versions with the debug function enabled. 63 64**System capability**: SystemCapability.HiviewDFX.HiLog 65 66**Parameters** 67 68| Name| Type | Mandatory| Description | 69| ------ | ------ | ---- | ------------------------------------------------------------ | 70| domain | number | Yes | Service domain of logs. The value ranges from **0x0** to **0xFFFF**. You can define the value within your application as required.| 71| 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.| 72| format | string | Yes | Format string used to output logs in a specified format. It can contain several parameters, 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>**.| 73| 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.| 74 75**Example** 76 77This 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. 78 79```js 80hilog.debug(0x0001, "testTag", "%{public}s World %{private}d", "hello", 3); 81``` 82 83If `"hello"` is filled in `%{public}s` and `3` in `%{private}d`, the output log is as follows: 84 85``` 8608-05 12:21:47.579 2695-2703/com.example.myapplication D 00001/testTag: hello World <private> 87``` 88 89## hilog.info 90 91info(domain: number, tag: string, format: string, ...args: any[]) : void 92 93Prints INFO logs. 94 95**System capability**: SystemCapability.HiviewDFX.HiLog 96 97**Parameters** 98 99| Name| Type | Mandatory| Description | 100| ------ | ------ | ---- | ------------------------------------------------------------ | 101| domain | number | Yes | Service domain of logs. The value ranges from **0x0** to **0xFFFF**. You can define the value within your application as required.| 102| 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.| 103| format | string | Yes | Format string used to output logs in a specified format. It can contain several parameters, 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>**.| 104| 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.| 105 106**Example** 107 108This 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. 109 110```js 111hilog.info(0x0001, "testTag", "%{public}s World %{private}d", "hello", 3); 112``` 113 114If `"hello"` is filled in `%{public}s` and `3` in `%{private}d`, the output log is as follows: 115 116``` 11708-05 12:21:47.579 2695-2703/com.example.myapplication I 00001/testTag: hello World <private> 118``` 119 120## hilog.warn 121 122warn(domain: number, tag: string, format: string, ...args: any[]) : void 123 124Prints WARN logs. 125 126**System capability**: SystemCapability.HiviewDFX.HiLog 127 128**Parameters** 129 130| Name| Type | Mandatory| Description | 131| ------ | ------ | ---- | ------------------------------------------------------------ | 132| domain | number | Yes | Service domain of logs. The value ranges from **0x0** to **0xFFFF**. You can define the value within your application as required.| 133| 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.| 134| format | string | Yes | Format string used to output logs in a specified format. It can contain several parameters, 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>**.| 135| 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.| 136 137**Example** 138 139This 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. 140 141```js 142hilog.warn(0x0001, "testTag", "%{public}s World %{private}d", "hello", 3); 143``` 144 145If `"hello"` is filled in `%{public}s` and `3` in `%{private}d`, the output log is as follows: 146 147``` 14808-05 12:21:47.579 2695-2703/com.example.myapplication W 00001/testTag: hello World <private> 149``` 150 151## hilog.error 152 153error(domain: number, tag: string, format: string, ...args: any[]) : void 154 155Prints ERROR logs. 156 157**System capability**: SystemCapability.HiviewDFX.HiLog 158 159**Parameters** 160 161| Name| Type | Mandatory| Description | 162| ------ | ------ | ---- | ------------------------------------------------------------ | 163| domain | number | Yes | Service domain of logs. The value ranges from **0x0** to **0xFFFF**. You can define the value within your application as required.| 164| 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.| 165| format | string | Yes | Format string used to output logs in a specified format. It can contain several parameters, 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>**.| 166| 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.| 167 168**Example** 169 170This 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. 171 172```js 173hilog.error(0x0001, "testTag", "%{public}s World %{private}d", "hello", 3); 174``` 175 176If `"hello"` is filled in `%{public}s` and `3` in `%{private}d`, the output log is as follows: 177 178``` 17908-05 12:21:47.579 2695-2703/com.example.myapplication E 00001/testTag: hello World <private> 180``` 181 182## hilog.fatal 183 184fatal(domain: number, tag: string, format: string, ...args: any[]) : void 185 186Prints FATAL logs. 187 188**System capability**: SystemCapability.HiviewDFX.HiLog 189 190**Parameters** 191 192| Name| Type | Mandatory| Description | 193| ------ | ------ | ---- | ------------------------------------------------------------ | 194| domain | number | Yes | Service domain of logs. The value ranges from **0x0** to **0xFFFF**. You can define the value within your application as required.| 195| 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.| 196| format | string | Yes | Format string used to output logs in a specified format. It can contain several parameters, 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>**.| 197| 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.| 198 199**Example** 200 201This 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. 202 203```js 204hilog.fatal(0x0001, "testTag", "%{public}s World %{private}d", "hello", 3); 205``` 206 207If `"hello"` is filled in `%{public}s` and `3` in `%{private}d`, the output log is as follows: 208 209``` 21008-05 12:21:47.579 2695-2703/com.example.myapplication F 00001/testTag: hello World <private> 211``` 212