EventTarget
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
EventTarget
介面定義了其實作的物件具有接收事件的能力,也可能擁有處理事件的監聽器。
除了最為常見的 Element
、Document
與 Window
繼承或實作了 EventTarget
介面之外,其它的物件還有 XMLHttpRequest
、AudioNode
、AudioContext
⋯ 等等。
許多 EventTarget
(包括 Element、Document 和 Window)除了透過 addEventListener()
方法外,還可藉由 DOM
物件的屬性(property)或 HTML 元素屬性(attribute)來設定事件處理器。
方法
EventTarget.addEventListener()
-
於
EventTarget
物件上註冊指定事件的監聽器。 EventTarget.removeEventListener()
-
移除
EventTarget
物件上的指定事件監聽器。 EventTarget.dispatchEvent()
-
對此
EventTarget
物件派送(dispatch)一個事件物件,也就是於此EventTarget
物件上觸發一個指定的事件物件實體。
Mozilla chrome code 的額外方法
Mozilla extensions for use by JS-implemented event targets to implement on properties. See also WebIDL bindings.
- void setEventHandler(DOMString type, EventHandler handler) Non-standard
- EventHandler getEventHandler(DOMString type) Non-standard
範例
Simple implementation of EventTarget
js
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];
event.target = this;
for (var i = 0, l = stack.length; i < l; i++) {
stack[i].call(this, event);
}
return !event.defaultPrevented;
};
規範
Specification |
---|
DOM Standard # interface-eventtarget |
瀏覽器相容性
BCD tables only load in the browser
參見
- Event reference - the events available in the platform.
- Event developer guide
Event
interface