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.

EventTarget()

Creates a new EventTarget object instance.

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.

Mozilla includes a couple of extensions for use by JS-implemented event targets to implement onevent properties.

See also WebIDL bindings.

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

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;
};

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