# @ohos.systemTimer

The **systemTimer** module provides system timer features. You can use the APIs of this module to implement the alarm clock and other timer services.

> **NOTE**
>
> - 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.
> - The APIs provided by this module are system APIs.

## Modules to Import


```js
import systemTimer from '@ohos.systemTimer';
```

## Constants

Provides the constants that define the supported timer types.

**System capability**: SystemCapability.MiscServices.Time

| Name               | Type  | Value  | Description                        |
| ------------------- | ------ | ---- | ---------------------------- |
| TIMER_TYPE_REALTIME | number | 1    | CPU time type. (The start time of the timer cannot be later than the current system time.)        |
| TIMER_TYPE_WAKEUP   | number | 2    | Wakeup type.                |
| TIMER_TYPE_EXACT    | number | 4    | Exact type.                |
| TIMER_TYPE_IDLE     | number | 8    | Idle type (not supported currently).|

 ## TimerOptions

Defines the initialization options for **createTimer**.

**System capability**: SystemCapability.MiscServices.Time

| Name     | Type                                         | Mandatory| Description                                                        |
| --------- | --------------------------------------------- | ---- | ------------------------------------------------------------ |
| type      | number                                        | Yes  | Timer type.<br>**1**: CPU time type. (The start time of the timer cannot be later than the current system time.)<br>**2**: wakeup type.<br>**4**: exact type.<br>**8**: idle type (not supported currently).|
| repeat    | boolean                                       | Yes  | Whether the timer is a repeating timer. The value **true** means that the timer is a repeating timer, and **false** means that the timer is a one-shot timer.                       |
| interval  | number                                        | No  | Repeat interval. For a repeating timer, the value must be greater than 5000 ms. For a one-shot timer, the value is **0**.|
| wantAgent | [WantAgent](js-apis-app-ability-wantAgent.md) | No  | **WantAgent** object of the notification to be sent when the timer expires. (An application MainAbility can be started, but not a Service ability.)|
| callback  | number                                        | Yes  | Callback used to return the timer ID.                            |


## systemTimer.createTimer

createTimer(options: TimerOptions, callback: AsyncCallback&lt;number&gt;): void

Creates a timer. This API uses an asynchronous callback to return the result.

**System API**: This is a system API.

**System capability**: SystemCapability.MiscServices.Time

**Parameters**

| Name  | Type                         | Mandatory| Description                                                        |
| -------- | ----------------------------- | ---- | ------------------------------------------------------------ |
| options  | [TimerOptions](#timeroptions) | Yes  | Timer initialization options, including the timer type, whether the timer is a repeating timer, interval, and **WantAgent** options.|
| callback | AsyncCallback&lt;number>      | Yes  | Callback used to return the timer ID.                                  |

**Example**

```js
export default {
    systemTimer () {
        let options = {
            type: systemTimer.TIMER_TYPE_REALTIME,
            repeat: false
        };
        try {
            systemTimer.createTimer(options, (error) => {
                if (error) {
                    console.info(`Failed to create timer. message:${error.message}, code:${error.code}`);
                    return;
                }
           		console.info(`Succeeded in creating timer.`);
        	});
        } catch(e) {
            console.info(`Failed to create timer. message:${e.message}, code:${e.code}`);
        }
    }
}
```

## systemTimer.createTimer

createTimer(options: TimerOptions): Promise&lt;number&gt;

Creates a timer. This API uses a promise to return the result.

**System API**: This is a system API.

**System capability**: SystemCapability.MiscServices.Time

**Parameters**

| Name | Type                         | Mandatory| Description                                                        |
| ------- | ----------------------------- | ---- | ------------------------------------------------------------ |
| options | [TimerOptions](#timeroptions) | Yes  | Timer initialization options, including the timer type, whether the timer is a repeating timer, interval, and **WantAgent** options.|

**Return value**

| Type                 | Description                         |
| --------------------- | ----------------------------- |
| Promise&lt;number&gt; | Promise used to return the timer ID.|

**Example**

```js
export default {
    systemTimer () {
        let options = {
            type: systemTimer.TIMER_TYPE_REALTIME,
            repeat:false
        };     
        try {
    		systemTimer.createTimer(options).then(() => {
    			console.info(`Succeeded in creating timer.`);
			}).catch((error) => {
    			console.info(`Failed to create timer. message:${error.message}, code:${error.code}`);
			});
        } catch(e) {
            console.info(`Failed to create timer. message:${e.message}, code:${e.code}`);
        }
    }
}
```

## systemTimer.startTimer

startTimer(timer: number, triggerTime: number, callback: AsyncCallback&lt;void&gt;): void

Starts a timer. This API uses an asynchronous callback to return the result.

**System API**: This is a system API.

**System capability**: SystemCapability.MiscServices.Time

**Parameters**

| Name     | Type                  | Mandatory| Description                          |
| ----------- | ---------------------- | ---- | ------------------------------ |
| timer       | number                 | Yes  | ID of the timer.                  |
| triggerTime | number                 | Yes  | Time when the timer is triggered, in milliseconds.|
| callback    | AsyncCallback&lt;void> | Yes  | Callback used to return the result.                    |

**Example**

```js
export default {
    async systemTimer () {
        let options = {
            type: systemTimer.TIMER_TYPE_REALTIME,
            repeat:false
        }
      let timerId = await systemTimer.createTimer(options)
      let triggerTime = new Date().getTime()
      triggerTime += 3000
      try {
          systemTimer.startTimer(timerId, triggerTime, (error) => {
              if (error) {
                  console.info(`Failed to start timer. message:${error.message}, code:${error.code}`);
                  return;
              }
              console.info(`Succeeded in starting timer.`);
          });
      } catch(e) {
          console.info(`Failed to start timer. message:${e.message}, code:${e.code}`);
      }
    }
}
```

## systemTimer.startTimer

startTimer(timer: number, triggerTime: number): Promise&lt;void&gt;

Starts a timer. This API uses a promise to return the result.

**System API**: This is a system API.

**System capability**: SystemCapability.MiscServices.Time

**Parameters**

| Name     | Type  | Mandatory| Description                          |
| ----------- | ------ | ---- | ------------------------------ |
| timer       | number | Yes  | ID of the timer.                  |
| triggerTime | number | Yes  | Time when the timer is triggered, in milliseconds.|

**Return value**

| Type          | Description                     |
| -------------- | ------------------------- |
| Promise\<void> | Promise that returns no value.|

**Example**

```js
export default {
    async systemTimer (){
        let options = {
            type: systemTimer.TIMER_TYPE_REALTIME,
            repeat:false
        }
        let timerId = await systemTimer.createTimer(options)
        let triggerTime = new Date().getTime()
        triggerTime += 3000
        try {
            systemTimer.startTimer(timerId, triggerTime).then(() => {
            	console.info(`Succeeded in starting timer.`);
       		}).catch((error) => {
            	console.info(`Failed to start timer. message:${error.message}, code:${error.code}`);
        	});
        } catch(e) {
            console.info(`Failed to start timer. message:${e.message}, code:${e.code}`);
        } 
    }
}
```

## systemTimer.stopTimer

stopTimer(timer: number, callback: AsyncCallback&lt;void&gt;): void

Stops a timer. This API uses an asynchronous callback to return the result.

**System API**: This is a system API.

**System capability**: SystemCapability.MiscServices.Time

**Parameters**

| Name  | Type                  | Mandatory| Description        |
| -------- | ---------------------- | ---- | ------------ |
| timer    | number                 | Yes  | ID of the timer.|
| callback | AsyncCallback&lt;void> | Yes  | Callback used to return the result.  |

**Example**

```js
export default {
    async systemTimer () {
        let options = {
            type: systemTimer.TIMER_TYPE_REALTIME,
            repeat:false
        }
        let timerId = await systemTimer.createTimer(options)
        let triggerTime = new Date().getTime()
        triggerTime += 3000
        systemTimer.startTimer(timerId, triggerTime)
        try {
            systemTimer.stopTimer(timerId, (error) => {
                if (error) {
                    console.info(`Failed to stop timer. message:${error.message}, code:${error.code}`);
                    return;
                }
                console.info(`Succeeded in stopping timer.`);
            });
        } catch(e) {
            console.info(`Failed to stop timer. message:${e.message}, code:${e.code}`);
        }
	}
}
```

## systemTimer.stopTimer

stopTimer(timer: number): Promise&lt;void&gt;

Stops a timer. This API uses a promise to return the result.

**System API**: This is a system API.

**System capability**: SystemCapability.MiscServices.Time

**Parameters**

| Name| Type  | Mandatory| Description        |
| ------ | ------ | ---- | ------------ |
| timer  | number | Yes  | ID of the timer.|

**Return value**

| Type          | Description                     |
| -------------- | ------------------------- |
| Promise\<void> | Promise that returns no value.|

**Example**

```js
export default {
    async systemTimer (){
        let options = {
            type: systemTimer.TIMER_TYPE_REALTIME,
            repeat:false
        }
        let timerId = await systemTimer.createTimer(options)
        let triggerTime = new Date().getTime()
        triggerTime += 3000
        systemTimer.startTimer(timerId, triggerTime)
        try {
            systemTimer.stopTimer(timerId).then(() => {
                console.info(`Succeeded in stopping timer.`);
            }).catch((error) => {
                console.info(`Failed to stop timer. message:${error.message}, code:${error.code}`);
            });
        } catch(e) {
            console.info(`Failed to stop timer. message:${e.message}, code:${e.code}`);
        }
    }
}
```

## systemTimer.destroyTimer

destroyTimer(timer: number, callback: AsyncCallback&lt;void&gt;): void

Destroys a timer. This API uses an asynchronous callback to return the result.

**System API**: This is a system API.

**System capability**: SystemCapability.MiscServices.Time

**Parameters**

| Name  | Type                  | Mandatory| Description        |
| -------- | ---------------------- | ---- | ------------ |
| timer    | number                 | Yes  | ID of the timer.|
| callback | AsyncCallback&lt;void> | Yes  | Callback used to return the result.  |

**Example**

```js
export default {
    async systemTimer () {
        let options = {
            type: systemTimer.TIMER_TYPE_REALTIME,
            repeat:false
        }
        let timerId = await systemTimer.createTimer(options)
        let triggerTime = new Date().getTime()
        triggerTime += 3000
        systemTimer.startTimer(timerId, triggerTime)
        systemTimer.stopTimer(timerId)
        try {
            systemTimer.destroyTimer(timerId, (error) => {
                if (error) {
                    console.info(`Failed to destroy timer. message:${error.message}, code:${error.code}`);
                    return;
                }
                console.info(`Succeeded in destroying timer.`);
        	});
        } catch(e) {
            console.info(`Failed to destroying timer. message:${e.message}, code:${e.code}`);
        }
    }
}
```

## systemTimer.destroyTimer

destroyTimer(timer: number): Promise&lt;void&gt;

Destroys a timer. This API uses a promise to return the result.

**System API**: This is a system API.

**System capability**: SystemCapability.MiscServices.Time

**Parameters**

| Name| Type  | Mandatory| Description        |
| ------ | ------ | ---- | ------------ |
| timer  | number | Yes  | ID of the timer.|

**Return value**

| Type          | Description                     |
| -------------- | ------------------------- |
| Promise\<void> | Promise that returns no value.|

**Example**

```js
export default {
    async systemTimer (){
        let options = {
            type: systemTimer.TIMER_TYPE_REALTIME,
            repeat:false
        }
        let timerId = await systemTimer.createTimer(options)
        let triggerTime = new Date().getTime()
        triggerTime += 3000
        systemTimer.startTimer(timerId, triggerTime)
        systemTimer.stopTimer(timerId)
        try {
            systemTimer.destroyTimer(timerId).then(() => {
            	 console.info(`Succeeded in destroying timer.`);
            }).catch((error) => {
                console.info(`Failed to destroy timer. message:${error.message}, code:${error.code}`);
            });
        } catch(e) {
            console.info(`Failed to destroying timer. message:${e.message}, code:${e.code}`);
        }
    }
}
```