# addErrorHandler()

Mounts an error handling function, to be called when the messaging framework encounters an error.

## Sample

Used within a JavaScript app uploaded as a static resource and referenced by `lightning:container`, this example mounts a message error handling function. In a React app, functions must be mounted to be part of the document-object model and rendered in the output.

```javascript
componentDidMount() {
  LCC.addErrorHandler(this.onMessageError);
}
```

## Arguments

| Name                                   | Type     | Description                                                                      |
| -------------------------------------- | -------- | -------------------------------------------------------------------------------- |
| `handler: (errorMsg: string) => void)` | function | The function that handles error messages encountered in the messaging framework. |

## Response

None.