当事件处理程序是原型函数时如何使用 removeEventListener？

Question

这是 question 的后续。问题是我对 removeEventListener 的调用不起作用。我必须在下面进行哪些更改才能使其正常工作？

我的自定义对象：

//Custom Editor Example with event listeners
var CE = function (id) {
    'use strict';

    // assume not a valid object
    this.isValid = false;
    this.element = document.getElementById(id);
    if (this.element !== null) {
        this.id = id;
        this.init();
        this.isValid = true;
    }
};


CE.prototype.addEvent = function (event, callback, caller) {
    'use strict';

    // check for modern browsers first
    if (typeof window.addEventListener === 'function') {
        return caller.element.addEventListener(event, function (e) {callback.call(caller, e); }, false);
    }
    // then for older versions of IE
    return this.element.attachEvent('on' + event, function (e) {callback.call(caller, window.event); });
};

CE.prototype.init = function () {
    'use strict';
    this.addEvent('keydown', this.onCustomKeyDown, this);
    // add other event listeners
};

这就是我尝试删除事件处理程序的方式：

CE.prototype.removeEvent = function (event, callback, caller) {
    'use strict';
    caller.element.removeEventListener(event, callback, false);
};


CE.prototype.destroy = function () {
    'use strict';
    this.removeEvent('keydown', this.onCustomKeyDown, this);
    // remove other event listeners
};

这是处理事件的原型函数的签名。

CE.prototype.onCustomKeyDown = function onCustomKeyDown(e) {

如果我没理解错的话，removeEventListener 不能用于删除作为匿名函数的事件处理程序。是这里的问题吗？我是否需要更改我的呼叫方式 addEventListener？

Answer 1

If I understand correctly, removeEventListener cannot be used to remove event handlers which are anonymous functions. Is that the issue here?

是的。添加的函数是匿名函数表达式，不是callback，所以用callback调用removeEventListener是不行的。

Do I need to change the way I'm calling addEventListener?

是的，您需要以某种方式保留对实际处理程序函数的引用，以便稍后可以将其传递给 removeEventListener。基本上有两种方法可以做到这一点：

使用闭包和 return 来自 addEvent 的 remover 函数将取消订阅。
在某处存储对事件处理程序的引用，以便您可以在调用 removeEvent 方法时通过回调识别它 - 并确保它不会泄漏。

Answer 2

谢谢@Bergi。

这是他回答中的选项 #2。你可以试试这个 JSFIDDLE.

//Custom Editor Example with event listeners
var CE = function (id) {
    'use strict';

    // assume not a valid object
    this.isValid = false;
    this.element = document.getElementById(id);
    if (this.element !== null) {
        this.id = id;
        this.customKeyDownHandler = null;
        this.customFocusHandler = null;
        this.init();
        this.isValid = true;
    }
};


/**
 * Initialize an event listener
 */
CE.prototype.addEvent = function (event, callback, caller) {
    'use strict';
    var handler;
    // check for modern browsers first
    if (typeof window.addEventListener === 'function') {
        this.element.addEventListener(event, handler = function (e) {
            callback.call(caller, e);
        }, false);
        return handler;
    }
    // then for older versions of IE
    this.element.attachEvent('on' + event, handler = function (e) {
        callback.call(caller, window.event);
    });
    return handler;
};


/**
 * init object
 */
CE.prototype.init = function () {
    'use strict';

    this.customKeyDownHandler = this.addEvent('keydown', this.onCustomKeyDown, this);
    this.customFocusHandler = this.addEvent('focus', this.onCustomFocus, this);
};

/**
 * remove an event listener
 */
CE.prototype.removeEvent = function (event, callback) {
    'use strict';
    this.element.removeEventListener(event, callback, false);
};


/**
 * destroy object
 */
CE.prototype.destroy = function () {
    'use strict';
    this.removeEvent('keydown', this.customKeyDownHandler);
    this.customKeyDownHandler = null;
    this.removeEvent('focus', this.customFocusHandler);
    this.customFocusHandler = null;
};

/**
 * keydown event handler responds to arrow keys
 */
CE.prototype.onCustomKeyDown = function (e) {
    'use strict';
    // if (e.keyCode === 46) { e.preventDefault(); alert("Del key is invalid"); return false; }
    alert("Hey, easy there! Not so hard!");
    return true;
};

/**
 * focus event handler
 */
CE.prototype.onCustomFocus = function (e) {
    'use strict';
    // if (e.keyCode === 46) { e.preventDefault(); alert("Del key is invalid"); return false; }
    alert("Welcome!");
    return true;
};


ce = new CE('myID'); // allocate custom editor

// do something

// input element will have default behavior, event handlers are removed
ce.destroy();

当事件处理程序是原型函数时如何使用 removeEventListener？

How to use removeEventListener when event handler is a prototype function?

javascript

event-handling