EventTarget - Web APIs 编辑

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.

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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.

Additional methods in Mozilla chrome codebase

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)

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

Browser compatibility

BCD tables only load in the browser

See also

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