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/DOM

EventTarget

EventTarget is an interface implemented by objects that can receive events and may have listeners for them.

Element, document, and window are the most common event targets, but other objects can be event targets too, for example XMLHttpRequest, AudioNode, AudioContext, and others.

Many event targets (including elements, documents, and windows) also support setting event handlers via on... properties and attributes.

Methods

EventTarget.addEventListener(): Register an event handler of a specific event type on the EventTarget.
EventTarget.removeEventListener(): Removes an event listener from the EventTarget.
EventTarget.dispatchEvent(): Dispatch an event to this EventTarget.

Additional methods for Mozilla chrome code

Mozilla extensions for use by JS-implemented event targets to implement on* properties. See also WebIDL bindings.

void setEventHandler(DOMString type, EventHandler handler)
EventHandler getEventHandler(DOMString type)

Example:

Simple implementation of EventTarget

var EventTarget = function() {
  this.listeners = {};
};

EventTarget.prototype.listeners = null;
EventTarget.prototype.addEventListener = function(type, callback) {
  if (!(type in this.listeners)) {
    this.listeners[type] = [];
  }
  this.listeners[type].push(callback);
};

EventTarget.prototype.removeEventListener = function(type, callback) {
  if (!(type in this.listeners)) {
    return;
  }
  var stack = this.listeners[type];
  for (var i = 0, l = stack.length; i < l; i++) {
    if (stack[i] === callback){
      stack.splice(i, 1);
      return;
    }
  }
};

EventTarget.prototype.dispatchEvent = function(event) {
  if (!(event.type in this.listeners)) {
    return true;
  }
  var stack = this.listeners[event.type];

  for (var i = 0, l = stack.length; i < l; i++) {
    stack[i].call(this, event);
  }
  return !event.defaultPrevented;
};

Specifications

Specification	Status	Comment
DOM The definition of 'EventTarget' in that specification.	Living Standard	No change.
Document Object Model (DOM) Level 3 Events Specification The definition of 'EventTarget' in that specification.	Obsolete	A few parameters are now optional (`listener`), or accepts the `null` value (`useCapture`).
Document Object Model (DOM) Level 2 Events Specification The definition of 'EventTarget' in that specification.	Obsolete	Initial definition.

Browser compatibility

Feature	Chrome	Edge	Firefox (Gecko)	Internet Explorer	Opera	Safari (WebKit)
Basic support	1.0	(Yes)	1.0 (1.7 or earlier)	9.0	7	1.0^[1] 10.1

Feature	Android	Edge	Firefox Mobile (Gecko)	IE Mobile	Opera Mobile	Safari Mobile
Basic support	1.0	(Yes)	1.0 (1)	9.0	6.0	1.0^[1] 10.1

[1] window.EventTarget does not exist.