# ErrorObserver

The ErrorObserver module defines an observer to listen for application errors. It can be used as an input parameter in [ErrorManager.on](js-apis-app-ability-errorManager.md#errormanageronerror) to listen for errors that occur in the current application.

> **NOTE**
> 
> The initial APIs of this module are supported since API version 9. Newly added APIs will be marked with a superscript to indicate their earliest API version.

## Modules to Import

```ts
import { errorManager } from '@kit.AbilityKit';
```

## ErrorObserver.onUnhandledException

onUnhandledException(errMsg: string): void;

Called when an unhandled exception occurs in the JS runtime.

**Atomic service API**: This API can be used in atomic services since API version 11.

**System capability**: SystemCapability.Ability.AbilityRuntime.Core

**Parameters**

| Name| Type| Mandatory| Description|
| -------- | -------- | -------- | -------- |
| errMsg | string | Yes| Message and error stack trace about the exception.|

**Example**

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

let observer: errorManager.ErrorObserver = {
  onUnhandledException(errorMsg) {
    console.error('onUnhandledException, errorMsg: ', errorMsg);
  }
};

try {
  errorManager.on('error', observer);
} catch (error) {
  console.error(`registerErrorObserver failed, error.code: ${(error as BusinessError).code}, error.message: ${(error as BusinessError).message}`);
}
```

## ErrorObserver.onException<sup>10+</sup>

onException?(errObject: Error): void;

Called when an exception occurs during the application running.

**Atomic service API**: This API can be used in atomic services since API version 11.

**System capability**: SystemCapability.Ability.AbilityRuntime.Core

**Parameters**

| Name| Type| Mandatory| Description|
| -------- | -------- | -------- | -------- |
| errObject | Error | Yes| Event name, message, and error stack of the exception.|

**Example**

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

let observer: errorManager.ErrorObserver = {
  onUnhandledException(errorMsg) {
    console.error('onUnhandledException, errorMsg: ', errorMsg);
  },
  onException(errorObj) {
    console.log('onException, name: ', errorObj.name);
    console.log('onException, message: ', errorObj.message);
    if (typeof (errorObj.stack) === 'string') {
      console.log('onException, stack: ', errorObj.stack);
    }
  }
};

try {
  errorManager.on('error', observer);
} catch (error) {
  console.error(`registerErrorObserver failed, error.code: ${(error as BusinessError).code}, error.message: ${(error as BusinessError).message}`);
}
```