EventTarget

EventTarget is a DOM 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 onevent properties and attributes.

Constructor

EventTarget()
Creates a new EventTarget object instance.

Methods

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

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].slice();

  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

BCD tables only load in the browser

See also