FindCommand (find-and-replace)

@ckeditor/ckeditor5-find-and-replace/src/findcommand

Properties

• inherited

  affectsData : booleanmodule:find-and-replace/findcommand~FindCommand#affectsData

  See source

  A flag indicating whether a command execution changes the editor data or not.

  Commands with affectsData set to false will not be automatically disabled in the read-only mode and other editor modes with restricted user write permissions.

  Note: You do not have to set it for your every command. It is true by default.

  Parameters

  affectsData : boolean

• readonly inherited

  editor : Editormodule:find-and-replace/findcommand~FindCommand#editor

  See source

  The editor on which this command will be used.

• inherited observable

  isEnabled : booleanmodule:find-and-replace/findcommand~FindCommand#isEnabled

  See source

  Flag indicating whether a command is enabled or disabled. A disabled command will do nothing when executed.

  A given command class should control this value by overriding the refresh() method.

  It is possible to disable a command "from outside" using forceDisabled method.

• inherited observable

  value : unknownmodule:find-and-replace/findcommand~FindCommand#value

  See source

  The value of the command. A given command class should define what it represents for it.

  For example, the 'bold' command's value indicates whether the selection starts in a bolded text. And the value of the 'link' command may be an object with link details.

  It is possible for a command to have no value (e.g. for stateless actions such as 'uploadImage').

  A given command class should control this value by overriding the refresh() method.

• protected inherited

  _isEnabledBasedOnSelection : booleanmodule:find-and-replace/findcommand~FindCommand#_isEnabledBasedOnSelection

  See source

  A flag indicating whether a command's isEnabled state should be changed depending on where the document selection is placed.

  By default, it is set to true. If the document selection is placed in a non-editable place (such as non-editable root), the command becomes disabled.

  The flag should be changed to false in a concrete command's constructor if the command should not change its isEnabled accordingly to the document selection.

• private

  _state : FindAndReplaceStatemodule:find-and-replace/findcommand~FindCommand#_state

  See source

  The find and replace state object used for command operations.

Methods

• constructor( editor, state )module:find-and-replace/findcommand~FindCommand#constructor

  See source

  Creates a new FindCommand instance.

  Parameters

  editor : Editor

  The editor on which this command will be used.

  state : FindAndReplaceState

  An object to hold plugin state.

• inherited

  bind( bindProperties ) → MultiBindChainmodule:find-and-replace/findcommand~FindCommand#bind:MANY_BIND

  See source

  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' | 'value' | 'execute' | 'isEnabled' | 'affectsData' | 'refresh' | 'editor' | 'forceDisabled' | 'clearForceDisabled'>

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

  Returns

  MultiBindChain

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

• inherited

  bind( bindProperty1, bindProperty2 ) → DualBindChain<K1, FindCommand[ K1 ], K2, FindCommand[ K2 ]>module:find-and-replace/findcommand~FindCommand#bind:DUAL_BIND

  See source

  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, FindCommand[ K1 ], K2, FindCommand[ K2 ]>

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

• inherited

  bind( bindProperty ) → SingleBindChain<K, FindCommand[ K ]>module:find-and-replace/findcommand~FindCommand#bind:SINGLE_BIND

  See source

  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, FindCommand[ K ]>

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

• inherited

  clearForceDisabled( id ) → voidmodule:find-and-replace/findcommand~FindCommand#clearForceDisabled

  See source

  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 ) → voidmodule:find-and-replace/findcommand~FindCommand#decorate

  See source

  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' | 'value' | 'execute' | 'isEnabled' | 'affectsData' | 'refresh' | 'editor' | 'forceDisabled' | 'clearForceDisabled'

  Name of the method to decorate.

  Returns

  void

• inherited

  delegate( events ) → EmitterMixinDelegateChainmodule:find-and-replace/findcommand~FindCommand#delegate

  See source

  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() → voidmodule:find-and-replace/findcommand~FindCommand#destroy

  See source

  Destroys the command.

  Returns

  void

• execute( callbackOrText, options ) → objectmodule:find-and-replace/findcommand~FindCommand#execute

  See source

  Executes the command.

  Parameters

  callbackOrText : string | FindCallback

  options : FindAttributes

  Options object.

  Defaults to {}

  Returns

  object

  Fires

  • execute

• inherited

  fire( eventOrInfo, args ) → GetEventInfo<TEvent>[ 'return' ]module:find-and-replace/findcommand~FindCommand#fire

  See source

  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 ) → voidmodule:find-and-replace/findcommand~FindCommand#forceDisabled

  See source

  Disables the command.

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

  Disabling and enabling a command:

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

  Command disabled by multiple features:

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

  Multiple disabling with the same identifier is redundant:

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

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

  Parameters

  id : string

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

  Returns

  void

• inherited

  listenTo( emitter, event, callback, [ options ] ) → voidmodule:find-and-replace/findcommand~FindCommand#listenTo:BASE_EMITTER

  See source

  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 ) → voidmodule:find-and-replace/findcommand~FindCommand#off

  See source

  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 ] ) → voidmodule:find-and-replace/findcommand~FindCommand#on

  See source

  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 ] ) → voidmodule:find-and-replace/findcommand~FindCommand#once

  See source

  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

• inherited

  refresh() → voidmodule:find-and-replace/findcommand~FindCommand#refresh

  See source

  Refreshes the command. The command should update its isEnabled and value properties in this method.

  This method is automatically called when any changes are applied to the document.

  Returns

  void

• inherited

  set( values ) → voidmodule:find-and-replace/findcommand~FindCommand#set:OBJECT

  See source

  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 ) → voidmodule:find-and-replace/findcommand~FindCommand#set:KEY_VALUE

  See source

  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 : FindCommand[ K ]

  The property's value.

  Returns

  void

• inherited

  stopDelegating( [ event ], [ emitter ] ) → voidmodule:find-and-replace/findcommand~FindCommand#stopDelegating

  See source

  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 ] ) → voidmodule:find-and-replace/findcommand~FindCommand#stopListening:BASE_STOP

  See source

  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 ) → voidmodule:find-and-replace/findcommand~FindCommand#unbind

  See source

  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' | 'value' | 'execute' | 'isEnabled' | 'affectsData' | 'refresh' | 'editor' | 'forceDisabled' | 'clearForceDisabled'>

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

  Returns

  void

Events

• inherited

  change:isEnabled( eventInfo, name, value, oldValue )module:find-and-replace/findcommand~FindCommand#event:change:isEnabled

  See source

  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:value( eventInfo, name, value, oldValue )module:find-and-replace/findcommand~FindCommand#event:change:value

  See source

  Fired when the value property changed value.

  Parameters

  eventInfo : EventInfo

  An object containing information about the fired event.

  name : string

  Name of the changed property (value).

  value : unknown

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

  oldValue : unknown

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

• inherited

  change:{property}( eventInfo, name, value, oldValue )module:find-and-replace/findcommand~FindCommand#event:change:{property}

  See source

  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

  execute( eventInfo, <anonymous> )module:find-and-replace/findcommand~FindCommand#event:execute

  See source

  Event fired by the execute method. The command action is a listener to this event so it's possible to change/cancel the behavior of the command by listening to this event.

  See decorate for more information and samples.

  Note: This event is fired even if command is disabled. However, it is automatically blocked by a high priority listener in order to prevent command execution.

  Parameters

  eventInfo : EventInfo

  An object containing information about the fired event.

  <anonymous> : Parameters<TObservable[ TName ]>

• inherited

  set:isEnabled( eventInfo, name, value, oldValue )module:find-and-replace/findcommand~FindCommand#event:set:isEnabled

  See source

  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:value( eventInfo, name, value, oldValue )module:find-and-replace/findcommand~FindCommand#event:set:value

  See source

  Fired when the value 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 (value).

  value : unknown

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

  oldValue : unknown

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

• inherited

  set:{property}( eventInfo, name, value, oldValue )module:find-and-replace/findcommand~FindCommand#event:set:{property}

  See source

  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.