EventTarget
Baseline
Widely available
*
This feature is well established and works across many devices and browser versions. It’s been available across browsers since 2015年7月.
* Some parts of this feature may have varying levels of support.
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
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 # interface-eventtarget |
瀏覽器相容性
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參見
- Event reference - the events available in the platform.
- Event developer guide
Eventinterface