EventTarget.removeEventListener()

EventTarget.removeEventListener() 方法可以移除先前由 addEventListener() 所註冊的事件監聽器。

語法

target.removeEventListener(type, listener[, options]);
target.removeEventListener(type, listener[, useCapture]);

參數

type

A string representing the event type to remove.

listener

The EventListener function to remove from the event target.

options 選擇性

An options object that specifies characteristics about the event listener. The available options are:

• capture: A Boolean that indicates that events of this type will be dispatched to the registered listener before being dispatched to any EventTarget beneath it in the DOM tree.  
• passive: A Boolean indicating that the listener will never call preventDefault(). If it does, the user agent should ignore it and generate a console warning.
• mozSystemGroup: Available only in code running in XBL or in Firefox' chrome, it is a Boolean defining if the listener is added to the system group.

useCapture 選擇性

Specifies whether the EventListener to be removed is registered as a capturing listener or not. If this parameter is absent, a default value of false is assumed.

If a listener is registered twice, one with capture and one without, remove each one separately. Removal of a capturing listener does not affect a non-capturing version of the same listener, and vice versa.

回傳值

無。

備註

If an EventListener is removed from an EventTarget while it is processing an event, it will not be triggered by the current actions. An EventListener will not be invoked for the event it was registered for after being removed, however it can be reattached.

Calling removeEventListener() with arguments that do not identify any currently registered EventListener on the EventTarget has no effect.

範例

This example shows how to add a click-based event listener and remove a mouseover-based event listener.

var body =
        document.querySelector('body'),
    clickTarget =
        document.getElementById('click-target'),
    mouseOverTarget =
        document.getElementById('mouse-over-target'),
    toggle = false;

function makeBackgroundYellow() {
    'use strict';

    if (toggle) {
        body.style.backgroundColor = 'white';
    } else {
        body.style.backgroundColor = 'yellow';
    }

    toggle = !toggle;
}

clickTarget.addEventListener('click',
    makeBackgroundYellow,
    false
);

mouseOverTarget.addEventListener('mouseover', function () {
    'use strict';

    clickTarget.removeEventListener('click',
        makeBackgroundYellow,
        false
    );
});

規範

瀏覽器相容性

[1] Although WebKit explicitly added "[optional]" to the useCapture parameter for Safari 5.1 and Chrome 13, it had been working before the change.

[2] Before Chrome 49, the type and listener parameters were optional.

[2] Prior to Firefox 6, the browser would throw an exception if the useCapture parameter was not explicitly false. Prior to Gecko 9.0 (Firefox 9.0 / Thunderbird 9.0 / SeaMonkey 2.6), addEventListener() would throw an exception if the listener parameter was null; now the method returns without error, but without doing anything.

[4] Opera 11.60 made the useCapture parameter optional (source).

[5] For backwards compatibility, browsers that support options allow the third parameter to be either options or Boolean.

Polyfill to support older browsers

addEventListener() and removeEventListener() are not present in older browsers. You can work around this by inserting the following code at the beginning of your scripts, allowing the use of addEventListener() and removeEventListener() in implementations that do not natively support it. However, this method will not work on Internet Explorer 7 or earlier, since extending the Element.prototype was not supported until Internet Explorer 8.

if (!Element.prototype.addEventListener) {
  var oListeners = {};
  function runListeners(oEvent) {
    if (!oEvent) { oEvent = window.event; }
    for (var iLstId = 0, iElId = 0, oEvtListeners = oListeners[oEvent.type]; iElId < oEvtListeners.aEls.length; iElId++) {
      if (oEvtListeners.aEls[iElId] === this) {
        for (iLstId; iLstId < oEvtListeners.aEvts[iElId].length; iLstId++) { oEvtListeners.aEvts[iElId][iLstId].call(this, oEvent); }
        break;
      }
    }
  }
  Element.prototype.addEventListener = function (sEventType, fListener /*, useCapture (will be ignored!) */) {
    if (oListeners.hasOwnProperty(sEventType)) {
      var oEvtListeners = oListeners[sEventType];
      for (var nElIdx = -1, iElId = 0; iElId < oEvtListeners.aEls.length; iElId++) {
        if (oEvtListeners.aEls[iElId] === this) { nElIdx = iElId; break; }
      }
      if (nElIdx === -1) {
        oEvtListeners.aEls.push(this);
        oEvtListeners.aEvts.push([fListener]);
        this["on" + sEventType] = runListeners;
      } else {
        var aElListeners = oEvtListeners.aEvts[nElIdx];
        if (this["on" + sEventType] !== runListeners) {
          aElListeners.splice(0);
          this["on" + sEventType] = runListeners;
        }
        for (var iLstId = 0; iLstId < aElListeners.length; iLstId++) {
          if (aElListeners[iLstId] === fListener) { return; }
        }     
        aElListeners.push(fListener);
      }
    } else {
      oListeners[sEventType] = { aEls: [this], aEvts: [ [fListener] ] };
      this["on" + sEventType] = runListeners;
    }
  };
  Element.prototype.removeEventListener = function (sEventType, fListener /*, useCapture (will be ignored!) */) {
    if (!oListeners.hasOwnProperty(sEventType)) { return; }
    var oEvtListeners = oListeners[sEventType];
    for (var nElIdx = -1, iElId = 0; iElId < oEvtListeners.aEls.length; iElId++) {
      if (oEvtListeners.aEls[iElId] === this) { nElIdx = iElId; break; }
    }
    if (nElIdx === -1) { return; }
    for (var iLstId = 0, aElListeners = oEvtListeners.aEvts[nElIdx]; iLstId < aElListeners.length; iLstId++) {
      if (aElListeners[iLstId] === fListener) { aElListeners.splice(iLstId, 1); }
    }
  };
}

參見

• EventTarget.addEventListener().
• EventTarget.detachEvent().