如何在闭包作用域中传递事件处理程序

Question

我正在尝试将事件处理程序添加到我的范围内。该功能addEvent工作正常。但是如果我像这样将函数传递给处理程序：

this.addEvent(window, "resize", self.resizeAd(this));

该函数不会传递给事件(The eventHandle is undefinded)，不知道为什么。

这是我的代码：

(function(window, document, undefined) {
    'use strict';
    var adTech = window.adTech = {
        get: function() {
            return _instance;
        },
        //Main entry point.
        init: function(options) {
            return _instance || new ADTECH(options);
        }
    };
    var ADTECH = function(options) {
        var defaultOptions = {
            adID : '5202402',
            hiddenClassName : 'hidden'
        };
        this.options = this.extend(options, defaultOptions);
        this.makeAd();
        _instance = this;
        return _instance;
    }
    ADTECH.prototype = {
        extend: function(source, target) {
            if (source == null) { return target; }
            for (var k in source) {
                if(source[k] != null && target[k] !== source[k]) {
                    target[k] = source[k];
                }
            }
            return target;
        },
        log: function(msg){
            if(window.console){
                console.log(msg);
            }
        },
        debounce:  function(func, wait, immediate) {
            var timeout;
            return function() {
                var context = this, args = arguments;
                var later = function() {
                    timeout = null;
                    if (!immediate) func.apply(context, args);
                };
                var callNow = immediate && !timeout;
                clearTimeout(timeout);
                timeout = setTimeout(later, wait);
                if (callNow) func.apply(context, args);
            };
        },
        addEvent: function (elem, type, eventHandle) {
            console.log("adEvent is undefined: ",eventHandle);
            if (elem == null || typeof(elem) == 'undefined') return;
            if (elem.addEventListener) {
                elem.addEventListener(type, eventHandle, false);
            } else if (elem.attachEvent) {
                elem.attachEvent("on" + type, eventHandle);
            } else {
                elem["on" + type] = eventHandle;
            }
        },
        // Function to resize div ad to take the full space we need / get
        resizeAd : function(this){
            this.log("resizeAd done.");
            var ad = document.getElementById(this.options.adID);
            this.log(ad);
            // do not work
            // this.debounce(function() {
            // console.log("tat:");
            // }, 250)
        },
        // insert ad
        makeAd: function () {
            this.addEvent(window, "resize", this.resizeAd(this));
            var self = this;
            //also do not work
            this.addEvent(window, "resize", self.resizeAd(this)); 
        }
    }
    // Singleton
    var _instance;
}(window, document));
var API = adTech.init();

Answer 1

修改 resizeAd 函数以返回函数。在这种情况下，也不需要将对象显式传递给该方法。此外，this是保留字，不能用作参数。

// ...
resizeAd: function(invokeLater) {
    // this is explicitly set based on the calling object.
    var obj = this;
    var helper = function ()
       obj.log("resizeAd done.");
       var ad = document.getElementById(obj.options.adID);
       obj.log(ad);
       obj.debounce(function() {
           console.log("tat:");
       }, 250)
    };
    // if invokeLater is a falsey value do the resizing right away
    // if it is truthy return helper so that it can be assigned as
    // an event handler
    return invokeLater ? helper : helper();
}, 
makeAd: function () {
    this.addEvent(window, "resize", this.resizeAd(true));
}
// note that you can still call resize normally.
this.resize();

在分配事件处理程序时调用函数时，您会收到The eventHandle is undefinded错误。

this.addEvent(window, "resize", this.resizeAd(this));

JavaScript 函数在未显式声明return时隐式返回 undefined。除非使用new调用函数，在这种情况下，新创建的对象将隐式返回。