# @ohos.systemTimer (System Timer) (System API)

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


```ts
import { systemTimer } from '@kit.BasicServicesKit';
```

## 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. (If the wakeup type is not set, the system does not wake up until it exits the sleep state.)|
| TIMER_TYPE_EXACT    | number | 4    | Exact type.                                     |
| TIMER_TYPE_IDLE     | number | 8    | Idle timer type (supported only for system services, but not applications)              |

 ## TimerOptions

Defines the initialization options for **createTimer**.

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

| Name       | Type                                         | Mandatory| Description                                                                                                                                                                                                  |
|-----------| --------------------------------------------- | ---- |------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| type      | number                                        | Yes  | Timer types. Use pipe (|) symbol|to combine two or more types.<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. (If an application is frozen, the timer is also frozen. In addition, the timer is controlled by a unified heartbeat. Therefore, even a timer of the exact type cannot be triggered at specified time.)<br>**8**: idle timer type (supported only for system services, but not applications).|
| repeat    | boolean                                       | Yes  | Whether the timer is a repeating timer.<br>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.<br>For a repeating timer, the minimum value of **interval** is 1s and the maximum value is 365 days. It is recommended that the value be greater than or equal to 5000 ms.<br>For a one-shot timer, the value is **0**.                                                                                                              |
| wantAgent | WantAgent | 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  | void                                          | No | Callback to be executed by the user.                                                                                                                                                                                         |


## 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 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.                                  |

**Error codes**

For details about the error codes, see [Time and Time Zone Service Error Codes](./errorcode-time.md).

| ID| Error Message                                                                                                                                        |
|-------|----------------------------------------------------------------------------------------------------------------------------------------------|
| 202   | Permission verification failed. A non-system application calls a system API.                                                                 |
| 401   | Parameter error. Possible causes: 1.Mandatory parameters are left unspecified; 2.Incorrect parameter types; 3.Parameter verification failed. |

**Example**

```ts
import { BusinessError } from '@kit.BasicServicesKit';

let options: systemTimer.TimerOptions = {
  type: systemTimer.TIMER_TYPE_REALTIME,
  repeat: false
};
try {
  systemTimer.createTimer(options, (error: BusinessError, timerId: Number) => {
    if (error) {
      console.info(`Failed to create a timer. Message: ${error.message}, code: ${error.code}`);
      return;
    }
    console.info(`Succeeded in creating a timer. timerId: ${timerId}`);
  });
} catch(e) {
  let error = e as BusinessError;
  console.info(`Failed to create a timer. Message: ${error.message}, code: ${error.code}`);
}
```

## systemTimer.createTimer

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

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


**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.|

**Error codes**

For details about the error codes, see [Time and Time Zone Service Error Codes](./errorcode-time.md).

| ID| Error Message                                                                                                       |
|-------|-------------------------------------------------------------------------------------------------------------|
| 202   | Permission verification failed. A non-system application calls a system API.                                |
| 401   | Parameter error. Possible causes: 1.Mandatory parameters are left unspecified; 2.Incorrect parameter types. |

**Example**

```ts
import { BusinessError } from '@kit.BasicServicesKit';

let options: systemTimer.TimerOptions = {
  type: systemTimer.TIMER_TYPE_REALTIME,
  repeat:false
};
try {
  systemTimer.createTimer(options).then((timerId: Number) => {
    console.info(`Succeeded in creating a timer. timerId: ${timerId}`);
  }).catch((error: BusinessError) => {
    console.info(`Failed to create a timer. Message: ${error.message}, code: ${error.code}`);
  });
} catch(e) {
  let error = e as BusinessError;
  console.info(`Failed to create a timer. Message: ${error.message}, code: ${error.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 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.<br>If **TIMER_TYPE_REALTIME** is set as the timer type, the value of **triggerTime** is the system startup time, which can be obtained by calling [systemDateTime.getUptime(STARTUP)](js-apis-date-time.md#systemdatetimegetuptime10).<br>If **TIMER_TYPE_REALTIME** is not set, the value of **triggerTime** is the wall time, which can be obtained by calling [systemDateTime.getTime()](js-apis-date-time.md#systemdatetimegettime10).|
| callback    | AsyncCallback&lt;void> | Yes  | Callback used to return the result.                                                                                                                                                                                                                                                       |

**Error codes**

For details about the error codes, see [Time and Time Zone Service Error Codes](./errorcode-time.md).

| ID| Error Message                                                                                                       |
|-------|-------------------------------------------------------------------------------------------------------------|
| 202   | Permission verification failed. A non-system application calls a system API.                                |
| 401   | Parameter error. Possible causes: 1.Mandatory parameters are left unspecified; 2.Incorrect parameter types. |

**Example**

```ts
import { BusinessError } from '@kit.BasicServicesKit';

let options: systemTimer.TimerOptions = {
  type: systemTimer.TIMER_TYPE_REALTIME,
  repeat:false
}
let triggerTime = new Date().getTime();
triggerTime += 3000;

try {
  systemTimer.createTimer(options).then((timerId: number) => {
    systemTimer.startTimer(timerId, triggerTime, (error: BusinessError) => {
      if (error) {
        console.info(`Failed to start the timer. Message: ${error.message}, code: ${error.code}`);
        return;
      }
      console.info(`Succeeded in starting the timer.`);
    });
    console.info(`Succeeded in creating a timer. timerId: ${timerId}`);
  }).catch((error: BusinessError) => {
    console.info(`Failed to create a timer. Message: ${error.message}, code: ${error.code}`);
  });
} catch(e) {
  let error = e as BusinessError;
  console.info(`Failed to create a timer. Message: ${error.message}, code: ${error.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 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.<br>If **TIMER_TYPE_REALTIME** is set as the timer type, the value of **triggerTime** is the system startup time, which can be obtained by calling [systemDateTime.getUptime(STARTUP)](js-apis-date-time.md#systemdatetimegetuptime10).<br>If **TIMER_TYPE_REALTIME** is not set, the value of **triggerTime** is the wall time, which can be obtained by calling [systemDateTime.getTime()](js-apis-date-time.md#systemdatetimegettime10).|

**Return value**

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

**Error codes**

For details about the error codes, see [Time and Time Zone Service Error Codes](./errorcode-time.md).

| ID| Error Message                                                                                                       |
|-------|-------------------------------------------------------------------------------------------------------------|
| 202   | Permission verification failed. A non-system application calls a system API.                                |
| 401   | Parameter error. Possible causes: 1.Mandatory parameters are left unspecified; 2.Incorrect parameter types. |

**Example**

```ts
import { BusinessError } from '@kit.BasicServicesKit';

let options: systemTimer.TimerOptions = {
  type: systemTimer.TIMER_TYPE_REALTIME,
  repeat:false
}
let triggerTime = new Date().getTime();
triggerTime += 3000;

try {
  systemTimer.createTimer(options).then((timerId: number) => {
    systemTimer.startTimer(timerId, triggerTime).then(() => {
      console.info(`Succeeded in starting the timer.`);
    }).catch((error: BusinessError) => {
      console.info(`Failed to start the timer. Message: ${error.message}, code: ${error.code}`);
    });
    console.info(`Succeeded in creating a timer. timerId: ${timerId}`);
  }).catch((error: BusinessError) => {
    console.info(`Failed to create a timer. Message: ${error.message}, code: ${error.code}`);
  });
} catch(e) {
  let error = e as BusinessError;
  console.info(`Failed to create a timer. Message: ${error.message}, code: ${error.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 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.  |

**Error codes**

For details about the error codes, see [Time and Time Zone Service Error Codes](./errorcode-time.md).

| ID| Error Message                                                                                                       |
|-------|-------------------------------------------------------------------------------------------------------------|
| 202   | Permission verification failed. A non-system application calls a system API.                                |
| 401   | Parameter error. Possible causes: 1.Mandatory parameters are left unspecified; 2.Incorrect parameter types. |

**Example**

```ts
import { BusinessError } from '@kit.BasicServicesKit';

let options: systemTimer.TimerOptions = {
  type: systemTimer.TIMER_TYPE_REALTIME,
  repeat:false
}
let triggerTime = new Date().getTime();
triggerTime += 3000;

try {
  systemTimer.createTimer(options).then((timerId: number) => {
    systemTimer.startTimer(timerId, triggerTime);
    systemTimer.stopTimer(timerId, (error: BusinessError) => {
      if (error) {
        console.info(`Failed to stop the timer. Message: ${error.message}, code: ${error.code}`);
        return;
      }
    console.info(`Succeeded in stopping the timer.`);
    });
    console.info(`Succeeded in creating a timer. timerId: ${timerId}`);
  }).catch((error: BusinessError) => {
    console.info(`Failed to create a timer. Message: ${error.message}, code: ${error.code}`);
  });
} catch(e) {
  let error = e as BusinessError;
  console.info(`Failed to create a timer. Message: ${error.message}, code: ${error.code}`);
}
```

## systemTimer.stopTimer

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

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

**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.|

**Error codes**

For details about the error codes, see [Time and Time Zone Service Error Codes](./errorcode-time.md).

| ID| Error Message                                                                                                       |
|-------|-------------------------------------------------------------------------------------------------------------|
| 202   | Permission verification failed. A non-system application calls a system API.                                |
| 401   | Parameter error. Possible causes: 1.Mandatory parameters are left unspecified; 2.Incorrect parameter types. |

**Example**

```ts
import { BusinessError } from '@kit.BasicServicesKit';

let options: systemTimer.TimerOptions = {
  type: systemTimer.TIMER_TYPE_REALTIME,
  repeat:false
}
let triggerTime = new Date().getTime();
triggerTime += 3000;

try {
  systemTimer.createTimer(options).then((timerId: number) => {
    systemTimer.startTimer(timerId, triggerTime);
    systemTimer.stopTimer(timerId).then(() => {
      console.info(`Succeeded in stopping the timer.`);
    }).catch((error: BusinessError) => {
      console.info(`Failed to stop the timer. Message: ${error.message}, code: ${error.code}`);
    });
    console.info(`Succeeded in creating a timer. timerId: ${timerId}`);
  }).catch((error: BusinessError) => {
    console.info(`Failed to create a timer. Message: ${error.message}, code: ${error.code}`);
  });
} catch(e) {
  let error = e as BusinessError;
  console.info(`Failed to create a timer. Message: ${error.message}, code: ${error.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 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.  |

**Error codes**

For details about the error codes, see [Time and Time Zone Service Error Codes](./errorcode-time.md).

| ID| Error Message                                                                                                       |
|-------|-------------------------------------------------------------------------------------------------------------|
| 202   | Permission verification failed. A non-system application calls a system API.                                |
| 401   | Parameter error. Possible causes: 1.Mandatory parameters are left unspecified; 2.Incorrect parameter types. |

**Example**

```ts
import { BusinessError } from '@kit.BasicServicesKit';

let options: systemTimer.TimerOptions = {
  type: systemTimer.TIMER_TYPE_REALTIME,
  repeat:false
}
let triggerTime = new Date().getTime();
triggerTime += 3000;

try {
  systemTimer.createTimer(options).then((timerId: number) => {
    systemTimer.startTimer(timerId, triggerTime);
    systemTimer.stopTimer(timerId);
    systemTimer.destroyTimer(timerId, (error: BusinessError) => {
      if (error) {
        console.info(`Failed to destroy the timer. Message: ${error.message}, code: ${error.code}`);
        return;
      }
    console.info(`Succeeded in destroying the timer.`);
    });
    console.info(`Succeeded in creating a timer. timerId: ${timerId}`);
  }).catch((error: BusinessError) => {
    console.info(`Failed to create a timer. Message: ${error.message}, code: ${error.code}`);
  });
} catch(e) {
  let error = e as BusinessError;
  console.info(`Failed to create a timer. Message: ${error.message}, code: ${error.code}`);
}
```

## systemTimer.destroyTimer

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

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

**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.|

**Error codes**

For details about the error codes, see [Time and Time Zone Service Error Codes](./errorcode-time.md).

| ID| Error Message                                                                                                       |
|-------|-------------------------------------------------------------------------------------------------------------|
| 202   | Permission verification failed. A non-system application calls a system API.                                |
| 401   | Parameter error. Possible causes: 1.Mandatory parameters are left unspecified; 2.Incorrect parameter types. |

**Example**

```ts
import { BusinessError } from '@kit.BasicServicesKit';

let options: systemTimer.TimerOptions = {
  type: systemTimer.TIMER_TYPE_REALTIME,
  repeat:false
}
let triggerTime = new Date().getTime();
triggerTime += 3000;

try {
  systemTimer.createTimer(options).then((timerId: number) => {
    systemTimer.startTimer(timerId, triggerTime);
    systemTimer.stopTimer(timerId);
    systemTimer.destroyTimer(timerId).then(() => {
      console.info(`Succeeded in destroying the timer.`);
    }).catch((error: BusinessError) => {
      console.info(`Failed to destroy the timer. Message: ${error.message}, code: ${error.code}`);
    });
    console.info(`Succeeded in creating a timer. timerId: ${timerId}`);
  }).catch((error: BusinessError) => {
    console.info(`Failed to create a timer. Message: ${error.message}, code: ${error.code}`);
  });
} catch(e) {
  let error = e as BusinessError;
  console.info(`Failed to create a timer. Message: ${error.message}, code: ${error.code}`);
}
```