无法解析Javascript对象方法这个参考

Question

我有我做了一个JS对象，有几个原型的功能，并从内部构造精细，采用这种美其名曰[功能]

但在后面的事件处理函数中，这指的是元素，而不是对象，我不知道如何解决这个问题：

它通过AddListener罚款，鼠标向下事件触发，导致启用/ disableDragging工作正常。但在该函数中，“this”是元素，而不是拖动器对象，所以我无法调用访问WindowCenter，DraggingBool或Add/RemoveListener事件。

从阅读起来，它看起来像我可能需要实现prototype.bind？但不知道如何重新安排我现有的代码来做到这一点。或者我改变其中一个函数来返回一个函数？

是的，我知道我可以在jQuery的做到这一点，做了很多次，只是想看看我是否能得到它与POJS :)

Dragger = function(element, draggingElement) { 
    this.Element = element; 
    this.DraggingElement = element; 
    this.WindowCenter; 
    this.DraggingBool = false; 

    this.AddListener(this.DraggingElement, "mousedown", this.enableDragging); 
    this.AddListener(this.DraggingElement, "mouseup", this.disableDragging); 
} 

Dragger.prototype.AddListener = function (element, eventType, listener, bubble) { 
    if (typeof (element) != "object" || typeof (listener) != "function") 
     return; 
    if (typeof (bubble) == "undefined") 
     var bubble = false; 
    eventType = eventType.toLowerCase(); 
    if (eventType.substr(0, 2) == "on") 
     eventType = eventType.substr(2); 
    if (window.addEventListener) { // Mozilla, Netscape, Firefox 
     element.addEventListener(eventType, listener, bubble); 
    } else if (window.attachEvent) { // IE 
     element.attachEvent("on" + eventType, listener); 
    } 
} 

Dragger.prototype.RemoveListener = function (element, eventType, listener) { 
    eventType = eventType.toLowerCase(); 
    if (eventType.substr(0, 2) == "on") 
     eventType = eventType.substr(2); 
    if (window.addEventListener) { // Mozilla, Netscape, Firefox 
     element.removeEventListener(eventType, listener, false); 
    } else if (window.attachEvent) { // IE 
     element.detachEvent("on" + eventType, listener); 
    } 
} 

Dragger.prototype.enableDragging = function (e) { 
    if (!e) var e = window.event; 
    //dont move for right click 
    if (e.which && e.which == 3) 
     return; 
    else if (e.button && e.button == 2) 
     return; 

    this.DraggingBool = true; 
    this.WindowCenter = new Point(e.pageX, e.pageY); 
    this.AddListener(document.body, "mouseover", this.mouseMoveListener); 
} 

Dragger.prototype.disableDragging = function() { 
    this.DraggingBool = false; 
    this.RemoveListener(document.body, "mouseover", this.mouseMoveListener); 
} 

Dragger.prototype.mouseMoveListener = function (e) { 
    if (!this.DraggingBool) 
     return; 
    if (!e) var e = window.event; 
    e.preventDefault(); 
    var newLoc = new Point(e.pageX, e.pageY); 
    var xDif = windowCenter.X - newLoc.X; 
    var yDif = windowCenter.Y - newLoc.Y; 
    this.Element.style.left = (this.Element.offsetLeft + xDif) + "px"; 
    this.Element.style.top = (this.Element.offsetTop + yDif) + "px"; 
    this.WindowCenter = newLoc; 
} 

Answer 1

这是使用addEventListener执行范围时，因为要去设置为节点，就像您使用node.onclick = foo一样。当您在IE中使用attachEvent时，执行范围将成为全局执行范围，即窗口。

解决此问题的一种方法是使用Function.call或Function.apply来指定您的喜好的执行范围。许多图书馆将宣布一个绑定功能，以解决这个问题，比如：

function bind(fn, context) { 
    return function() { 
    return fn.apply(context, arguments); 
    }; 
} 

this.AddListener(this.DraggingElement, "mousedown", 
    bind(this.enableDragging, this)); 

你也可以添加一个上下文参数到您的addListener功能，并在那里做了结合。

Ecmascript 5有一个内置的绑定方法。

Answer 2

Function.prototype.bind = function() { 
    if (arguments.length < 2 && arguments[0] === undefined) { 
    return this; 
    } 

    var thisObj = this, 
    args = Array.prototype.slice.call(arguments), 

    obj = args.shift(); 

    return function() { 
    return thisObj.apply(obj, args.concat(Array.prototype.slice.call(arguments))); 
    }; 

    }; 



    Function.bind = function() { 
    var args = Array.prototype.slice.call(arguments); 
    return Function.prototype.bind.apply(args.shift(), args); 

    } 

Dragger = function(element, draggingElement) { 
    this.Element = element; 
    this.DraggingElement = element; 
    this.WindowCenter; 
    this.DraggingBool = false; 

    this.AddListener(this.DraggingElement, "mousedown", this.enableDragging,this); 
    this.AddListener(this.DraggingElement, "mouseup", this.disableDragging,this); 
} 

Dragger.prototype.AddListener = function (element, eventType, listener, bubble,dragger_obj) { 
    if (typeof (element) != "object" || typeof (listener) != "function") 
     return; 
    if (typeof (bubble) == "undefined") 
     var bubble = false; 
    eventType = eventType.toLowerCase(); 
    if (eventType.substr(0, 2) == "on") 
     eventType = eventType.substr(2); 
    if (window.addEventListener) { // Mozilla, Netscape, Firefox 
     element.addEventListener(eventType, listener.bind(dragger_obj), bubble); 
    } else if (window.attachEvent) { // IE 
     element.attachEvent("on" + eventType, listener.bind(dragger_obj)); 
    } 
} 

Dragger.prototype.RemoveListener = function (element, eventType, listener,dragger_obj) { 
    eventType = eventType.toLowerCase(); 
    if (eventType.substr(0, 2) == "on") 
     eventType = eventType.substr(2); 
    if (window.addEventListener) { // Mozilla, Netscape, Firefox 
     element.removeEventListener(eventType, listener.bind(dragger_obj), false); 
    } else if (window.attachEvent) { // IE 
     element.detachEvent("on" + eventType, listener.bind(dragger_obj)); 
    } 
} 

Dragger.prototype.enableDragging = function (e) { 
    if (!e) var e = window.event; 
    //dont move for right click 
    if (e.which && e.which == 3) 
     return; 
    else if (e.button && e.button == 2) 
     return; 

    this.DraggingBool = true; 
    this.WindowCenter = new Point(e.pageX, e.pageY); 
    this.AddListener(document.body, "mouseover", this.mouseMoveListener,this); 
} 

Dragger.prototype.disableDragging = function() { 
    this.DraggingBool = false; 
    this.RemoveListener(document.body, "mouseover", this.mouseMoveListener,this); 
} 

Dragger.prototype.mouseMoveListener = function (e) { 
    if (!this.DraggingBool) 
     return; 
    if (!e) var e = window.event; 
    e.preventDefault(); 
    var newLoc = new Point(e.pageX, e.pageY); 
    var xDif = windowCenter.X - newLoc.X; 
    var yDif = windowCenter.Y - newLoc.Y; 
    this.Element.style.left = (this.Element.offsetLeft + xDif) + "px"; 
    this.Element.style.top = (this.Element.offsetTop + yDif) + "px"; 
    this.WindowCenter = newLoc; 
}