# Class: EventHandler

## Core. EventHandler

#### new EventHandler()

### Methods

#### addEventListener(type, fn [, options])

  Add a handler to the given event name

  ##### Parameters:

  Name | Type | Argument | Description
  --- | --- | --- | ---
  `type` | string | number |  | The name of the event to listen to
  `fn` | function |  | The handler to be called when the event is triggered
  `options` | object | <optional> | Optional options object for addEventListener ###### Properties
  Name | Type | Description
  --- | --- | ---
  `once` | boolean | If true then the handler will be called only once

  ##### Returns:

  Returns the object that 'addEventListener' is being called on
  Type
    object

  ##### Example

      annotManager.addEventListener('annotationChanged', (annotations, action) => {
        ...
      });

#### off( [type] [, fn])

  Remove a handler of the given event name

  ##### Parameters:

  Name | Type | Argument | Description
  --- | --- | --- | ---
  `type` | string | number | <optional> | The name of the event to remove the handler of. If type is undefined, all the handlers of the object will be removed
  `fn` | function | <optional> | The handler associated with this event to be removed. If fn is undefined, all the handlers of the given event name will be removed

  Deprecated:
    - Since version 8.0. Use removeEventListener instead.

  ##### Returns:

  Returns the object that 'off' is being called on
  Type
    object

  ##### Example

      annotManager.off();
      annotManager.off('annotationChanged');
      annotManager.off('annotationChanged', fn);

#### on(type, fn)

  Add a handler to the given event name

  ##### Parameters:

  Name | Type | Description
  --- | --- | ---
  `type` | string | number | The name of the event to listen to
  `fn` | function | The handler to be called when the event is triggered

  Deprecated:
    - Since version 8.0. Use addEventListener instead.

  ##### Returns:

  Returns the object that 'on' is being called on
  Type
    object

  ##### Example

      annotManager.on('annotationChanged', (annotations, action) => {
        ...
      });

#### one(type, fn)

  Same as 'on' except the handler will be called only once

  ##### Parameters:

  Name | Type | Description
  --- | --- | ---
  `type` | string | number | The name of the event to listen to
  `fn` | function | The handler to be called when the event is triggered

  Deprecated:
    - Since version 8.0. Use addEventListener with {'once': true} as options instead.

  ##### Returns:

  Returns the object that 'one' is being called on
  Type
    object

  ##### Example

      annotManager.one('annotationChanged', (annotations, action) => {
       ...
      });

#### removeEventListener( [type] [, fn])

  Remove a handler of the given event name

  ##### Parameters:

  Name | Type | Argument | Description
  --- | --- | --- | ---
  `type` | string | number | <optional> | The name of the event to remove the handler of. If type is undefined, all the handlers of the object will be removed
  `fn` | function | <optional> | The handler associated with this event to be removed. If fn is undefined, all the handlers of the given event name will be removed

  ##### Returns:

  Returns the object that 'removeEventListener' is being called on
  Type
    object

  ##### Example

      annotManager.removeEventListener();
      annotManager.removeEventListener('annotationChanged');
      annotManager.removeEventListener('annotationChanged', fn);

#### trigger(type [, data])

  Calls the handlers of the event name with given data

  ##### Parameters:

  Name | Type | Argument | Description
  --- | --- | --- | ---
  `type` | string | number |  | event name of which the handlers will be called.
  `data` | * | <optional> | data that will be passed to the handlers. If data is an array, it will be spread and then passed to the handlers

  ##### Returns:

  Returns the object that 'trigger' is being called on
  Type
    object

  ##### Example

      annotManager.trigger('annotationChanged');
      annotManager.trigger('annotationChanged', [[annotation], 'add', {}]);

#### Search results