# ObservableChangeEvent

typedef

Fired when a property changed value.

```typescript
observable.set( 'prop', 1 );

observable.on<ObservableChangeEvent<number>>( 'change:prop', ( evt, propertyName, newValue, oldValue ) => {
	console.log( `${ propertyName } has changed from ${ oldValue } to ${ newValue }` );
} );

observable.prop = 2; // -> 'prop has changed from 1 to 2'
```

[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/observablemixin.ts#L1190)

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## Type parameters

### `TValue: any`

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## Properties

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### `args: [ name: string, value: TValue, oldValue: TValue ]`

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### `` name: 'change' | `change:${ string }` ``

#### Value

`object`

## Fired by

* [Observable#change:{property}](module_utils_observablemixin-Observable.md#event-change:%7Bproperty%7D)

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Full index of the CKEditor 5 API reference: [llms.txt](llms.txt)