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 this.removeEventListener(type, callback);
    }
  }
};

EventTarget.prototype.dispatchEvent = function(event) {
  if(!(event.type in this.listeners)) {
    return;
  }
  var stack = this.listeners[event.type];
  event.target = this;
  for(var i = 0, l = stack.length; i < l; i++) {
      stack[i].call(this, event);
  }
};

Specifications

Browser compatibility

We're converting our compatibility data into a machine-readable JSON format. This compatibility table still uses the old format, because we haven't yet converted the data it contains. Find out how you can help!

[1] window.EventTarget does not exist.

See Also

• Event reference - the events available in the platform.
• Event developer guide
• Event interface