# AnnotationsUIs

class

A repository of annotations UIs.

The main entry point for [registering](#function-register) UIs and activating the annotations UI(s), which display annotation views.

To register a custom annotations UI use following code in the annotations UI plugin `init()` function:

```typescript
const annotationsUIs = editor.plugins.get( 'annotationsUIs' );

annotationsUIs.register( customAnnotationsUIPlugin );
```

Note that the custom annotations UI must implement [the `AnnotationsUI` interface](module_comments_annotations_annotationsuis-AnnotationsUI.md).

To activate an annotations UI, use the [`switchTo( uiName )`](#function-switchTo) method. This method activates the given UI and deactivates all the other UIs. All annotations will be handled by the activated UI.

It is also possible to activate multiple annotations UIs at the same time and make the UIs handle different sets of annotations. To do that, use the [`activate( uiName, filter )`](#function-activate) method.

```typescript
// Suggestions annotations are shown inline in a balloon:
annotationsUIs.activate( 'inline', annotation => annotation.type.startsWith( 'suggestion' ) );

// At the same time, comments annotations are shown in a sidebar:
annotationsUIs.activate( 'wideSidebar', annotation => annotation.type === 'comment' );
```

Limitations:

* Some annotations UI plugins might collide with each other (like [`NarrowSidebar`](module_comments_annotations_narrowsidebar-NarrowSidebar.md) and [`WideSidebar`](module_comments_annotations_widesidebar-WideSidebar.md) that operates on the same sidebar). They cannot be activated at the same time.
* It is not possible to display the same annotation in two different annotations UIs. In this scenario an error will be thrown.

<a id="properties">

## Properties

<a id="member-activeUIs">

### `activeUIs: Set<string>`

A set of names of the active annotations UIs.

To activate the annotations UI, use [`activate`](#function-activate) or [`switchTo`](#function-switchTo) methods.

<a id="member-context">

### `context: ContextInterface` _(readonly)_

The context or editor instance.

#### Static properties

<a id="static-member-isContextPlugin">

### `isContextPlugin: true` _(readonly)_

<a id="static-member-isOfficialPlugin">

### `isOfficialPlugin: true` _(readonly)_

<a id="static-member-isPremiumPlugin">

### `isPremiumPlugin: true` _(readonly)_

<a id="static-member-pluginName">

### `pluginName: 'AnnotationsUIs'` _(readonly)_

<a id="static-member-requires">

### `requires: readonly [ PluginConstructor<Editor> & new ( context: Editor ) => Annotations ]` _(readonly)_

<a id="methods">

## Methods

<a id="function-constructor">

### `constructor( context )`

#### Parameters

* `context: Editor | Context`

<a id="function-activate">

### `activate( uiName, filter ) → void`

Activates an annotations UI.

Note that the custom annotations UI should be [registered](#function-register) before the activation.

The `filter` parameter can be used to display on some of the annotations in the given annotations UI. Thanks to that, all annotations can be split into various annotations UIs.

The `filter` function takes an [`Annotation`](module_comments_annotations_annotation-Annotation.md) instance as the first and only parameter, and should return `true` if that annotation should be placed in the given annotations UI.

#### Parameters

* `uiName: string`

  The name of the annotations UI to activate.

* `filter: ( annotation: Annotation ) => boolean`

  The annotation filter function. If not specified, the UI will use all annotations.

  Defaults to `...`

#### Returns

* `void`

<a id="function-bind:MANY_BIND">

### `bind( bindProperties ) → ObservableMultiBindChain` _(inherited)_

Binds [observable properties](#function-set:KEY_VALUE) to other objects implementing the [`Observable`](module_utils_observablemixin-Observable.md) interface.

Read more in the [dedicated](../framework/deep-dive/observables.md#property-bindings) guide covering the topic of property bindings with some additional examples.

Consider two objects: a `button` and an associated `command` (both `Observable`).

A simple property binding could be as follows:

```typescript
button.bind( 'isEnabled' ).to( command, 'isEnabled' );
```

or even shorter:

```typescript
button.bind( 'isEnabled' ).to( command );
```

which works in the following way:

* `button.isEnabled` **instantly equals** `command.isEnabled`,
* whenever `command.isEnabled` changes, `button.isEnabled` will immediately reflect its value.

**Note**: To release the binding, use [`unbind`](module_utils_observablemixin-Observable.md#function-unbind).

You can also "rename" the property in the binding by specifying the new name in the `to()` chain:

```typescript
button.bind( 'isEnabled' ).to( command, 'isWorking' );
```

It is possible to bind more than one property at a time to shorten the code:

```typescript
button.bind( 'isEnabled', 'value' ).to( command );
```

which corresponds to:

```typescript
button.bind( 'isEnabled' ).to( command );
button.bind( 'value' ).to( command );
```

The binding can include more than one observable, combining multiple data sources in a custom callback:

```typescript
button.bind( 'isEnabled' ).to( command, 'isEnabled', ui, 'isVisible',
	( isCommandEnabled, isUIVisible ) => isCommandEnabled && isUIVisible );
```

Using a custom callback allows processing the value before passing it to the target property:

```typescript
button.bind( 'isEnabled' ).to( command, 'value', value => value === 'heading1' );
```

It is also possible to bind to the same property in an array of observables. To bind a `button` to multiple commands (also `Observables`) so that each and every one of them must be enabled for the button to become enabled, use the following code:

```typescript
button.bind( 'isEnabled' ).toMany( [ commandA, commandB, commandC ], 'isEnabled',
	( isAEnabled, isBEnabled, isCEnabled ) => isAEnabled && isBEnabled && isCEnabled );
```

#### Parameters

* `bindProperties: Array<'off' | 'set' | 'bind' | 'unbind' | 'decorate' | 'stopListening' | 'on' | 'once' | 'listenTo' | 'fire' | 'delegate' | 'stopDelegating' | 'destroy' | 'register' | 'context' | 'init' | 'deactivateAll' | 'activeUIs' | 'uisData' | 'isActive' | 'activate' | 'hasActive' | 'deactivate' | 'switchTo' | 'refilterAnnotations' | 'defaultFilter'>`

  Observable properties that will be bound to other observable(s).

#### Returns

* `ObservableMultiBindChain`

  The bind chain with the `to()` and `toMany()` methods.

<a id="function-bind:DUAL_BIND">

### `bind( bindProperty1, bindProperty2 ) → ObservableDualBindChain<K1, AnnotationsUIs[ K1 ], K2, AnnotationsUIs[ K2 ]>` _(inherited)_

Binds [observable properties](#function-set:KEY_VALUE) to other objects implementing the [`Observable`](module_utils_observablemixin-Observable.md) interface.

Read more in the [dedicated](../framework/deep-dive/observables.md#property-bindings) guide covering the topic of property bindings with some additional examples.

Consider two objects: a `button` and an associated `command` (both `Observable`).

A simple property binding could be as follows:

```typescript
button.bind( 'isEnabled' ).to( command, 'isEnabled' );
```

or even shorter:

```typescript
button.bind( 'isEnabled' ).to( command );
```

which works in the following way:

* `button.isEnabled` **instantly equals** `command.isEnabled`,
* whenever `command.isEnabled` changes, `button.isEnabled` will immediately reflect its value.

**Note**: To release the binding, use [`unbind`](module_utils_observablemixin-Observable.md#function-unbind).

You can also "rename" the property in the binding by specifying the new name in the `to()` chain:

```typescript
button.bind( 'isEnabled' ).to( command, 'isWorking' );
```

It is possible to bind more than one property at a time to shorten the code:

```typescript
button.bind( 'isEnabled', 'value' ).to( command );
```

which corresponds to:

```typescript
button.bind( 'isEnabled' ).to( command );
button.bind( 'value' ).to( command );
```

The binding can include more than one observable, combining multiple data sources in a custom callback:

```typescript
button.bind( 'isEnabled' ).to( command, 'isEnabled', ui, 'isVisible',
	( isCommandEnabled, isUIVisible ) => isCommandEnabled && isUIVisible );
```

Using a custom callback allows processing the value before passing it to the target property:

```typescript
button.bind( 'isEnabled' ).to( command, 'value', value => value === 'heading1' );
```

It is also possible to bind to the same property in an array of observables. To bind a `button` to multiple commands (also `Observables`) so that each and every one of them must be enabled for the button to become enabled, use the following code:

```typescript
button.bind( 'isEnabled' ).toMany( [ commandA, commandB, commandC ], 'isEnabled',
	( isAEnabled, isBEnabled, isCEnabled ) => isAEnabled && isBEnabled && isCEnabled );
```

#### Type parameters

* * `K1`
  * `K2`

#### Parameters

* `bindProperty1: K1`

  Observable property that will be bound to other observable(s).

* `bindProperty2: K2`

  Observable property that will be bound to other observable(s).

#### Returns

* `ObservableDualBindChain<K1, AnnotationsUIs[ K1 ], K2, AnnotationsUIs[ K2 ]>`

  The bind chain with the `to()` and `toMany()` methods.

<a id="function-bind:SINGLE_BIND">

### `bind( bindProperty ) → ObservableSingleBindChain<K, AnnotationsUIs[ K ]>` _(inherited)_

Binds [observable properties](#function-set:KEY_VALUE) to other objects implementing the [`Observable`](module_utils_observablemixin-Observable.md) interface.

Read more in the [dedicated](../framework/deep-dive/observables.md#property-bindings) guide covering the topic of property bindings with some additional examples.

Consider two objects: a `button` and an associated `command` (both `Observable`).

A simple property binding could be as follows:

```typescript
button.bind( 'isEnabled' ).to( command, 'isEnabled' );
```

or even shorter:

```typescript
button.bind( 'isEnabled' ).to( command );
```

which works in the following way:

* `button.isEnabled` **instantly equals** `command.isEnabled`,
* whenever `command.isEnabled` changes, `button.isEnabled` will immediately reflect its value.

**Note**: To release the binding, use [`unbind`](module_utils_observablemixin-Observable.md#function-unbind).

You can also "rename" the property in the binding by specifying the new name in the `to()` chain:

```typescript
button.bind( 'isEnabled' ).to( command, 'isWorking' );
```

It is possible to bind more than one property at a time to shorten the code:

```typescript
button.bind( 'isEnabled', 'value' ).to( command );
```

which corresponds to:

```typescript
button.bind( 'isEnabled' ).to( command );
button.bind( 'value' ).to( command );
```

The binding can include more than one observable, combining multiple data sources in a custom callback:

```typescript
button.bind( 'isEnabled' ).to( command, 'isEnabled', ui, 'isVisible',
	( isCommandEnabled, isUIVisible ) => isCommandEnabled && isUIVisible );
```

Using a custom callback allows processing the value before passing it to the target property:

```typescript
button.bind( 'isEnabled' ).to( command, 'value', value => value === 'heading1' );
```

It is also possible to bind to the same property in an array of observables. To bind a `button` to multiple commands (also `Observables`) so that each and every one of them must be enabled for the button to become enabled, use the following code:

```typescript
button.bind( 'isEnabled' ).toMany( [ commandA, commandB, commandC ], 'isEnabled',
	( isAEnabled, isBEnabled, isCEnabled ) => isAEnabled && isBEnabled && isCEnabled );
```

#### Type parameters

* `K`

#### Parameters

* `bindProperty: K`

  Observable property that will be bound to other observable(s).

#### Returns

* `ObservableSingleBindChain<K, AnnotationsUIs[ K ]>`

  The bind chain with the `to()` and `toMany()` methods.

<a id="function-deactivate">

### `deactivate( uiName ) → void`

Deactivates annotations UI with given name.

#### Parameters

* `uiName: string`

  The name of the annotations UI to deactivate.

#### Returns

* `void`

<a id="function-deactivateAll">

### `deactivateAll() → void`

Deactivates all annotations UIs.

#### Returns

* `void`

<a id="function-decorate">

### `decorate( methodName ) → void` _(inherited)_

Turns the given methods of this object into event-based ones. This means that the new method will fire an event (named after the method) and the original action will be plugged as a listener to that event.

Read more in the [dedicated](../framework/deep-dive/observables.md#decorating-object-methods) guide covering the topic of decorating methods with some additional examples.

Decorating the method does not change its behavior (it only adds an event), but it allows to modify it later on by listening to the method's event.

For example, to cancel the method execution the event can be [stopped](module_utils_eventinfo-EventInfo.md#member-stop):

```typescript
class Foo extends ObservableMixin() {
	constructor() {
		super();
		this.decorate( 'method' );
	}

	method() {
		console.log( 'called!' );
	}
}

const foo = new Foo();
foo.on( 'method', ( evt ) => {
	evt.stop();
}, { priority: 'high' } );

foo.method(); // Nothing is logged.
```

**Note**: The high [priority](module_utils_priorities-PriorityString.md) listener has been used to execute this particular callback before the one which calls the original method (which uses the "normal" priority).

It is also possible to change the returned value:

```typescript
foo.on( 'method', ( evt ) => {
	evt.return = 'Foo!';
} );

foo.method(); // -> 'Foo'
```

Finally, it is possible to access and modify the arguments the method is called with:

```typescript
method( a, b ) {
	console.log( `${ a }, ${ b }`  );
}

// ...

foo.on( 'method', ( evt, args ) => {
	args[ 0 ] = 3;

	console.log( args[ 1 ] ); // -> 2
}, { priority: 'high' } );

foo.method( 1, 2 ); // -> '3, 2'
```

#### Parameters

* `methodName: 'off' | 'set' | 'bind' | 'unbind' | 'decorate' | 'stopListening' | 'on' | 'once' | 'listenTo' | 'fire' | 'delegate' | 'stopDelegating' | 'destroy' | 'register' | 'context' | 'init' | 'deactivateAll' | 'activeUIs' | 'uisData' | 'isActive' | 'activate' | 'hasActive' | 'deactivate' | 'switchTo' | 'refilterAnnotations' | 'defaultFilter'`

  Name of the method to decorate.

#### Returns

* `void`

<a id="function-defaultFilter">

### `defaultFilter() → boolean`

A default pass-by filter function that returns `true` for all annotations to be used when no filter for UI is provided.

#### Returns

* `boolean`

<a id="function-delegate">

### `delegate( events ) → EmitterMixinDelegateChain` _(inherited)_

Delegates selected events to another [`Emitter`](module_utils_emittermixin-Emitter.md). For instance:

```typescript
emitterA.delegate( 'eventX' ).to( emitterB );
emitterA.delegate( 'eventX', 'eventY' ).to( emitterC );
```

then `eventX` is delegated (fired by) `emitterB` and `emitterC` along with `data`:

```typescript
emitterA.fire( 'eventX', data );
```

and `eventY` is delegated (fired by) `emitterC` along with `data`:

```typescript
emitterA.fire( 'eventY', data );
```

#### Parameters

* `events: Array<string>`

  Event names that will be delegated to another emitter.

#### Returns

* `EmitterMixinDelegateChain`

<a id="function-destroy">

### `destroy() → void`

Destroys the plugin.

**Note:** This method is optional. A plugin instance does not need to have it defined.

#### Returns

* `void`

<a id="function-fire">

### `fire( eventOrInfo, args ) → GetEventInfo<TEvent>[ 'return' ]` _(inherited)_

Fires an event, executing all callbacks registered for it.

The first parameter passed to callbacks is an [`EventInfo`](module_utils_eventinfo-EventInfo.md) object, followed by the optional `args` provided in the `fire()` method call.

#### Type parameters

* `TEvent: extends BaseEvent`

  The type describing the event. See [`BaseEvent`](module_utils_emittermixin-BaseEvent.md).

#### Parameters

* `eventOrInfo: GetNameOrEventInfo<TEvent>`

  The name of the event or `EventInfo` object if event is delegated.

* `args: TEvent[ 'args' ]`

  Additional arguments to be passed to the callbacks.

#### Returns

* `GetEventInfo<TEvent>[ 'return' ]`

  By default the method returns `undefined`. However, the return value can be changed by listeners through modification of the [`evt.return`](module_utils_eventinfo-EventInfo.md#member-return)'s property (the event info is the first param of every callback).

<a id="function-hasActive">

### `hasActive() → boolean`

Returns `true` if at least one registered UI is active.

#### Returns

* `boolean`

<a id="function-init">

### `init() → void`

#### Returns

* `void`

<a id="function-isActive">

### `isActive( uiName ) → boolean`

Returns `true` if the given UI is active.

#### Parameters

* `uiName: string`

#### Returns

* `boolean`

<a id="function-listenTo:BASE_EMITTER">

### `listenTo( emitter, event, callback, options? ) → void` _(inherited)_

Registers a callback function to be executed when an event is fired in a specific (emitter) object.

Events can be grouped in namespaces using `:`. When namespaced event is fired, it additionally fires all callbacks for that namespace.

```typescript
// myEmitter.on( ... ) is a shorthand for myEmitter.listenTo( myEmitter, ... ).
myEmitter.on( 'myGroup', genericCallback );
myEmitter.on( 'myGroup:myEvent', specificCallback );

// genericCallback is fired.
myEmitter.fire( 'myGroup' );
// both genericCallback and specificCallback are fired.
myEmitter.fire( 'myGroup:myEvent' );
// genericCallback is fired even though there are no callbacks for "foo".
myEmitter.fire( 'myGroup:foo' );
```

An event callback can [stop the event](module_utils_eventinfo-EventInfo.md#member-stop) and set the [return value](module_utils_eventinfo-EventInfo.md#member-return) of the [`fire`](#function-fire) method.

#### Type parameters

* `TEvent: extends BaseEvent`

  The type describing the event. See [`BaseEvent`](module_utils_emittermixin-BaseEvent.md).

#### Parameters

* `emitter: Emitter`

  The object that fires the event.

* `event: TEvent[ 'name' ]`

  The name of the event.

* `callback: GetCallback<TEvent>`

  The function to be called on event.

* `options?: GetCallbackOptions<TEvent>`

  Additional options.

#### Returns

* `void`

<a id="function-off">

### `off( event, callback ) → void` _(inherited)_

Stops executing the callback on the given event. Shorthand for [`this.stopListening( this, event, callback )`](#function-stopListening:BASE_STOP).

#### Parameters

* `event: string`

  The name of the event.

* `callback: Function`

  The function to stop being called.

#### Returns

* `void`

<a id="function-on">

### `on( event, callback, options? ) → void` _(inherited)_

Registers a callback function to be executed when an event is fired.

Shorthand for [`this.listenTo( this, event, callback, options )`](#function-listenTo:BASE_EMITTER) (it makes the emitter listen on itself).

#### Type parameters

* `TEvent: extends BaseEvent`

  The type descibing the event. See [`BaseEvent`](module_utils_emittermixin-BaseEvent.md).

#### Parameters

* `event: TEvent[ 'name' ]`

  The name of the event.

* `callback: GetCallback<TEvent>`

  The function to be called on event.

* `options?: GetCallbackOptions<TEvent>`

  Additional options.

#### Returns

* `void`

<a id="function-once">

### `once( event, callback, options? ) → void` _(inherited)_

Registers a callback function to be executed on the next time the event is fired only. This is similar to calling [`on`](#function-on) followed by [`off`](#function-off) in the callback.

#### Type parameters

* `TEvent: extends BaseEvent`

  The type descibing the event. See [`BaseEvent`](module_utils_emittermixin-BaseEvent.md).

#### Parameters

* `event: TEvent[ 'name' ]`

  The name of the event.

* `callback: GetCallback<TEvent>`

  The function to be called on event.

* `options?: GetCallbackOptions<TEvent>`

  Additional options.

#### Returns

* `void`

<a id="function-refilterAnnotations">

### `refilterAnnotations() → void`

Refilters annotations to proper UIs based on filters provided earlier during the [annotations UIs activation](#function-activate).

This method should be used if the annotations UIs filtering functions return different results than before for some annotations. It only reattaches these annotations, which should change their UIs.

#### Returns

* `void`

<a id="function-register">

### `register( uiName, annotationsUI ) → void`

Registers an annotations UI. It might be one of:

* [`WideSidebar`](module_comments_annotations_widesidebar-WideSidebar.md),
* [`NarrowSidebar`](module_comments_annotations_narrowsidebar-NarrowSidebar.md),
* [`InlineAnnotations`](module_comments_annotations_inlineannotations-InlineAnnotations.md).

It is possible to provide your own, custom annotations UI plugin. It has to implement [the `AnnotationsUI` interface](module_comments_annotations_annotationsuis-AnnotationsUI.md).

#### Parameters

* `uiName: string`

  Annotations UI name.

* `annotationsUI: AnnotationsUI<ContextPlugin | Plugin>`

  Annotations UI plugin instance.

#### Returns

* `void`

<a id="function-set:OBJECT">

### `set( values ) → void` _(inherited)_

Creates and sets the value of an observable properties of this object. Such a property becomes a part of the state and is observable.

It accepts a single object literal containing key/value pairs with properties to be set.

This method throws the `observable-set-cannot-override` error if the observable instance already has a property with the given property name. This prevents from mistakenly overriding existing properties and methods, but means that `foo.set( 'bar', 1 )` may be slightly slower than `foo.bar = 1`.

In TypeScript, those properties should be declared in class using `declare` keyword. In example:

```typescript
public declare myProp1: number;
public declare myProp2: string;

constructor() {
	this.set( {
		'myProp1: 2,
		'myProp2: 'foo'
	} );
}
```

#### Parameters

* `values: object & object`

  An object with `name=>value` pairs.

#### Returns

* `void`

<a id="function-set:KEY_VALUE">

### `set( name, value ) → void` _(inherited)_

Creates and sets the value of an observable property of this object. Such a property becomes a part of the state and is observable.

This method throws the `observable-set-cannot-override` error if the observable instance already has a property with the given property name. This prevents from mistakenly overriding existing properties and methods, but means that `foo.set( 'bar', 1 )` may be slightly slower than `foo.bar = 1`.

In TypeScript, those properties should be declared in class using `declare` keyword. In example:

```typescript
public declare myProp: number;

constructor() {
	this.set( 'myProp', 2 );
}
```

#### Type parameters

* `K`

#### Parameters

* `name: K`

  The property's name.

* `value: AnnotationsUIs[ K ]`

  The property's value.

#### Returns

* `void`

<a id="function-stopDelegating">

### `stopDelegating( event?, emitter? ) → void` _(inherited)_

Stops delegating events. It can be used at different levels:

* To stop delegating all events.
* To stop delegating a specific event to all emitters.
* To stop delegating a specific event to a specific emitter.

#### Parameters

* `event?: string`

  The name of the event to stop delegating. If omitted, stops it all delegations.

* `emitter?: Emitter`

  (requires `event`) The object to stop delegating a particular event to. If omitted, stops delegation of `event` to all emitters.

#### Returns

* `void`

<a id="function-stopListening:BASE_STOP">

### `stopListening( emitter?, event?, callback? ) → void` _(inherited)_

Stops listening for events. It can be used at different levels:

* To stop listening to a specific callback.
* To stop listening to a specific event.
* To stop listening to all events fired by a specific object.
* To stop listening to all events fired by all objects.

#### Parameters

* `emitter?: Emitter`

  The object to stop listening to. If omitted, stops it for all objects.

* `event?: string`

  (Requires the `emitter`) The name of the event to stop listening to. If omitted, stops it for all events from `emitter`.

* `callback?: Function`

  (Requires the `event`) The function to be removed from the call list for the given `event`.

#### Returns

* `void`

<a id="function-switchTo">

### `switchTo( uiName ) → void`

Switches the annotations UI to the one with given name.

It preserves the currently active annotation.

#### Parameters

* `uiName: string`

  The name of the annotations UI to switch to.

#### Returns

* `void`

<a id="function-unbind">

### `unbind( unbindProperties ) → void` _(inherited)_

Removes the binding created with [`bind`](#function-bind:SINGLE_BIND).

```typescript
// Removes the binding for the 'a' property.
A.unbind( 'a' );

// Removes bindings for all properties.
A.unbind();
```

#### Parameters

* `unbindProperties: Array<'off' | 'set' | 'bind' | 'unbind' | 'decorate' | 'stopListening' | 'on' | 'once' | 'listenTo' | 'fire' | 'delegate' | 'stopDelegating' | 'destroy' | 'register' | 'context' | 'init' | 'deactivateAll' | 'activeUIs' | 'uisData' | 'isActive' | 'activate' | 'hasActive' | 'deactivate' | 'switchTo' | 'refilterAnnotations' | 'defaultFilter'>`

  Observable properties to be unbound. All the bindings will be released if no properties are provided.

#### Returns

* `void`

<a id="events">

## Events

<a id="event-change:%7Bproperty%7D">

### `change:{property}( eventInfo, name, value, oldValue )` _(inherited)_

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'
```

#### Parameters

* `eventInfo: EventInfo`

  An object containing information about the fired event.

* `name: string`

  The property name.

* `value: TValue`

  The new property value.

* `oldValue: TValue`

  The previous property value.

<a id="event-set:%7Bproperty%7D">

### `set:{property}( eventInfo, name, value, oldValue )` _(inherited)_

Fired when a property value is going to be set but is not set yet (before the `change` event is fired).

You can control the final value of the property by using the [event's `return` property](module_utils_eventinfo-EventInfo.md#member-return).

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

observable.on<ObservableSetEvent<number>>( 'set:prop', ( evt, propertyName, newValue, oldValue ) => {
	console.log( `Value is going to be changed from ${ oldValue } to ${ newValue }` );
	console.log( `Current property value is ${ observable[ propertyName ] }` );

	// Let's override the value.
	evt.return = 3;
} );

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

observable.prop = 2; // -> 'Value is going to be changed from 1 to 2'
					 // -> 'Current property value is 1'
					 // -> 'Value has changed from 1 to 3'
```

**Note:** The event is fired even when the new value is the same as the old value.

#### Parameters

* `eventInfo: EventInfo`

  An object containing information about the fired event.

* `name: string`

  The property name.

* `value: TValue`

  The new property value.

* `oldValue: TValue`

  The previous property value.

---

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