Class

TwoStepCaretMovement (typing)

@ckeditor/ckeditor5-typing/src/twostepcaretmovement

class

This plugin enables the two-step caret (phantom) movement behavior for registered attributes on arrow right () and left () key press.

Thanks to this (phantom) caret movement the user is able to type before/after as well as at the beginning/end of an attribute.

Note: This plugin support right–to–left (Arabic, Hebrew, etc.) content by mirroring its behavior but for the sake of simplicity examples showcase only left–to–right use–cases.

Forward movement

"Entering" an attribute:

When this plugin is enabled and registered for the a attribute and the selection is right before it (at the attribute boundary), pressing the right arrow key will not move the selection but update its attributes accordingly:

  • When enabled:
foo{}<$text a="true">bar</$text>
<kbd>→</kbd>
foo<$text a="true">{}bar</$text>
  • When disabled:
foo{}<$text a="true">bar</$text>
<kbd>→</kbd>
foo<$text a="true">b{}ar</$text>
"Leaving" an attribute:
  • When enabled:
<$text a="true">bar{}</$text>baz
<kbd>→</kbd>
<$text a="true">bar</$text>{}baz
  • When disabled:
<$text a="true">bar{}</$text>baz
<kbd>→</kbd>
<$text a="true">bar</$text>b{}az

Backward movement

  • When enabled:
<$text a="true">bar</$text>{}baz
<kbd>←</kbd>
<$text a="true">bar{}</$text>baz
  • When disabled:
<$text a="true">bar</$text>{}baz
<kbd>←</kbd>
<$text a="true">ba{}r</$text>b{}az

Multiple attributes

  • When enabled and many attributes starts or ends at the same position:
<$text a="true" b="true">bar</$text>{}baz
<kbd>←</kbd>
<$text a="true" b="true">bar{}</$text>baz
  • When enabled and one procedes another:
<$text a="true">bar</$text><$text b="true">{}bar</$text>
<kbd>←</kbd>
<$text a="true">bar{}</$text><$text b="true">bar</$text>

Filtering

Properties

  • readonly

    _isGravityOverridden : boolean

    true when the gravity is overridden for the plugin.

  • readonly inherited

    editor : Editor

    The editor instance.

    Note that most editors implement the ui property. However, editors with an external UI (i.e. Bootstrap-based) or a headless editor may not have this property or throw an error when accessing it.

    Because of above, to make plugins more universal, it is recommended to split features into:

    • The "editing" part that uses the Editor class without ui property.
    • The "UI" part that uses the Editor class and accesses ui property.
  • inherited observable

    isEnabled : boolean

    Flag indicating whether a plugin is enabled or disabled. A disabled plugin will not transform text.

    Plugin can be simply disabled like that:

    // Disable the plugin so that no toolbars are visible.
    editor.plugins.get( 'TextTransformation' ).isEnabled = false;
    

    You can also use forceDisabled method.

  • private

    _isNextGravityRestorationSkipped : boolean

    A flag indicating that the automatic gravity restoration should not happen upon the next gravity restoration. event-change:range event.

  • private

    _overrideUid : null | string

    The current UID of the overridden gravity, as returned by overrideSelectionGravity.

  • private

    attributes : Set<string>

    A set of attributes to handle.

Static properties

  • readonly inherited static

    isContextPlugin : false

  • readonly static

    pluginName : 'TwoStepCaretMovement'

Methods

  • constructor( editor )

    Parameters

    editor : Editor
  • inherited

    bind( bindProperty1, bindProperty2 ) → DualBindChain<K1, TwoStepCaretMovement[ K1 ], K2, TwoStepCaretMovement[ K2 ]>

    Binds observable properties to other objects implementing the Observable interface.

    Read more in the dedicated 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:

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

    or even shorter:

    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.

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

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

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

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

    which corresponds to:

    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:

    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:

    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:

    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

    DualBindChain<K1, TwoStepCaretMovement[ K1 ], K2, TwoStepCaretMovement[ K2 ]>

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

  • inherited

    bind( bindProperties ) → MultiBindChain

    Binds observable properties to other objects implementing the Observable interface.

    Read more in the dedicated 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:

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

    or even shorter:

    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.

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

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

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

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

    which corresponds to:

    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:

    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:

    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:

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

    Parameters

    bindProperties : Array<'off' | 'on' | 'once' | 'listenTo' | 'stopListening' | 'fire' | 'delegate' | 'stopDelegating' | 'set' | 'bind' | 'unbind' | 'decorate' | 'destroy' | 'init' | 'editor' | 'isEnabled' | 'forceDisabled' | 'clearForceDisabled' | 'registerAttribute'>

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

    Returns

    MultiBindChain

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

  • inherited

    bind( bindProperty ) → SingleBindChain<K, TwoStepCaretMovement[ K ]>

    Binds observable properties to other objects implementing the Observable interface.

    Read more in the dedicated 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:

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

    or even shorter:

    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.

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

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

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

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

    which corresponds to:

    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:

    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:

    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:

    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

    SingleBindChain<K, TwoStepCaretMovement[ K ]>

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

  • inherited

    clearForceDisabled( id ) → void

    Clears forced disable previously set through forceDisabled. See forceDisabled.

    Parameters

    id : string

    Unique identifier, equal to the one passed in forceDisabled call.

    Returns

    void
  • inherited

    decorate( methodName ) → void

    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 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:

    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 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:

    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:

    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' | 'on' | 'once' | 'listenTo' | 'stopListening' | 'fire' | 'delegate' | 'stopDelegating' | 'set' | 'bind' | 'unbind' | 'decorate' | 'destroy' | 'init' | 'editor' | 'isEnabled' | 'forceDisabled' | 'clearForceDisabled' | 'registerAttribute'

    Name of the method to decorate.

    Returns

    void
  • inherited

    delegate( events ) → EmitterMixinDelegateChain

    Delegates selected events to another Emitter. For instance:

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

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

    emitterA.fire( 'eventX', data );
    

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

    emitterA.fire( 'eventY', data );
    

    Parameters

    events : Array<string>

    Event names that will be delegated to another emitter.

    Returns

    EmitterMixinDelegateChain
  • inherited

    destroy() → void

    Destroys the plugin.

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

    Returns

    void
  • inherited

    fire( eventOrInfo, args ) → GetEventInfo<TEvent>[ 'return' ]

    Fires an event, executing all callbacks registered for it.

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

    Type parameters

    TEvent : extends BaseEvent

    The type describing the event. See BaseEvent.

    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's property (the event info is the first param of every callback).

  • inherited

    forceDisabled( id ) → void

    Disables the plugin.

    Plugin may be disabled by multiple features or algorithms (at once). When disabling a plugin, unique id should be passed (e.g. feature name). The same identifier should be used when enabling back the plugin. The plugin becomes enabled only after all features enabled it back.

    Disabling and enabling a plugin:

    plugin.isEnabled; // -> true
    plugin.forceDisabled( 'MyFeature' );
    plugin.isEnabled; // -> false
    plugin.clearForceDisabled( 'MyFeature' );
    plugin.isEnabled; // -> true
    

    Plugin disabled by multiple features:

    plugin.forceDisabled( 'MyFeature' );
    plugin.forceDisabled( 'OtherFeature' );
    plugin.clearForceDisabled( 'MyFeature' );
    plugin.isEnabled; // -> false
    plugin.clearForceDisabled( 'OtherFeature' );
    plugin.isEnabled; // -> true
    

    Multiple disabling with the same identifier is redundant:

    plugin.forceDisabled( 'MyFeature' );
    plugin.forceDisabled( 'MyFeature' );
    plugin.clearForceDisabled( 'MyFeature' );
    plugin.isEnabled; // -> true
    

    Note: some plugins or algorithms may have more complex logic when it comes to enabling or disabling certain plugins, so the plugin might be still disabled after clearForceDisabled was used.

    Parameters

    id : string

    Unique identifier for disabling. Use the same id when enabling back the plugin.

    Returns

    void
  • init() → void

    Returns

    void
  • inherited

    listenTo( emitter, event, callback, [ options ] ) → void

    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.

    // 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 and set the return value of the fire method.

    Type parameters

    TEvent : extends BaseEvent

    The type describing the event. See BaseEvent.

    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
  • inherited

    off( event, callback ) → void

    Stops executing the callback on the given event. Shorthand for this.stopListening( this, event, callback ).

    Parameters

    event : string

    The name of the event.

    callback : Function

    The function to stop being called.

    Returns

    void
  • inherited

    on( event, callback, [ options ] ) → void

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

    Shorthand for this.listenTo( this, event, callback, options ) (it makes the emitter listen on itself).

    Type parameters

    TEvent : extends BaseEvent

    The type descibing the event. See BaseEvent.

    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
  • inherited

    once( event, callback, [ options ] ) → void

    Registers a callback function to be executed on the next time the event is fired only. This is similar to calling on followed by off in the callback.

    Type parameters

    TEvent : extends BaseEvent

    The type descibing the event. See BaseEvent.

    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
  • registerAttribute( attribute ) → void

    Registers a given attribute for the two-step caret movement.

    Parameters

    attribute : string

    Name of the attribute to handle.

    Returns

    void
  • inherited

    set( values ) → void

    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:

    public declare myProp1: number;
    public declare myProp2: string;
    
    constructor() {
    	this.set( {
    		'myProp1: 2,
    		'myProp2: 'foo'
    	} );
    }
    

    Parameters

    values : object

    An object with name=>value pairs.

    Returns

    void
  • inherited

    set( name, value ) → void

    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:

    public declare myProp: number;
    
    constructor() {
    	this.set( 'myProp', 2 );
    }
    

    Type parameters

    K

    Parameters

    name : K

    The property's name.

    value : TwoStepCaretMovement[ K ]

    The property's value.

    Returns

    void
  • inherited

    stopDelegating( [ event ], [ emitter ] ) → void

    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
  • inherited

    stopListening( [ emitter ], [ event ], [ callback ] ) → void

    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
  • inherited

    unbind( unbindProperties ) → void

    Removes the binding created with bind.

    // Removes the binding for the 'a' property.
    A.unbind( 'a' );
    
    // Removes bindings for all properties.
    A.unbind();
    

    Parameters

    unbindProperties : Array<'off' | 'on' | 'once' | 'listenTo' | 'stopListening' | 'fire' | 'delegate' | 'stopDelegating' | 'set' | 'bind' | 'unbind' | 'decorate' | 'destroy' | 'init' | 'editor' | 'isEnabled' | 'forceDisabled' | 'clearForceDisabled' | 'registerAttribute'>

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

    Returns

    void
  • private

    _enableClickingAfterNode() → void

    Starts listening to event-mousedown and event-selectionChange and puts the selection before/after a 2-step node if clicked at the beginning/ending of the 2-step node.

    The purpose of this action is to allow typing around the 2-step node directly after a click.

    See https://github.com/ckeditor/ckeditor5/issues/1016.

    Returns

    void
  • private

    _enableInsertContentSelectionAttributesFixer() → void

    Starts listening to event-insertContent and corrects the model selection attributes if the selection is at the end of a two-step node after inserting the content.

    The purpose of this action is to improve the overall UX because the user is no longer "trapped" by the two-step attribute of the selection, and they can type a "clean" (linkHref–less) text right away.

    See https://github.com/ckeditor/ckeditor5/issues/6053.

    Returns

    void
  • private

    _handleBackwardMovement( data ) → boolean

    Updates the document selection and the view according to the two–step caret movement state when moving backwards. Executed upon keypress in the View.

    Parameters

    data : DomEventData<Event>

    Data of the key press.

    Returns

    boolean

    true when the handler prevented caret movement

  • private

    _handleDeleteContentAfterNode() → void

    Starts listening to deleteContent and checks whether removing a content right after the tow-step attribute.

    If so, the selection should not preserve the two-step attribute. However, if the TwoStepCaretMovement plugin is active and the selection has the two-step attribute due to overridden gravity (at the end), the two-step attribute should stay untouched.

    The purpose of this action is to allow removing the link text and keep the selection outside the link.

    See https://github.com/ckeditor/ckeditor5/issues/7521.

    Returns

    void
  • private

    _handleForwardMovement( data ) → boolean

    Updates the document selection and the view according to the two–step caret movement state when moving forwards. Executed upon keypress in the View.

    Parameters

    data : DomEventData<Event>

    Data of the key press.

    Returns

    boolean

    true when the handler prevented caret movement.

  • private

    _overrideGravity() → void

    Overrides the gravity using the model writer and stores the information about this fact in the _overrideUid.

    A shorthand for overrideSelectionGravity.

    Returns

    void
  • private

    _restoreGravity() → void

    Restores the gravity using the model writer.

    A shorthand for restoreSelectionGravity.

    Returns

    void

Events

  • inherited

    change:isEnabled( eventInfo, name, value, oldValue )

    Fired when the isEnabled property changed value.

    Parameters

    eventInfo : EventInfo

    An object containing information about the fired event.

    name : string

    Name of the changed property (isEnabled).

    value : boolean

    New value of the isEnabled property with given key or null, if operation should remove property.

    oldValue : boolean

    Old value of the isEnabled property with given key or null, if property was not set before.

  • inherited

    change:{property}( eventInfo, name, value, oldValue )

    Fired when a property changed value.

    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.

  • inherited

    set:isEnabled( eventInfo, name, value, oldValue )

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

    Parameters

    eventInfo : EventInfo

    An object containing information about the fired event.

    name : string

    Name of the changed property (isEnabled).

    value : boolean

    New value of the isEnabled property with given key or null, if operation should remove property.

    oldValue : boolean

    Old value of the isEnabled property with given key or null, if property was not set before.

  • inherited

    set:{property}( eventInfo, name, value, oldValue )

    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.

    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.