文章排版有问题，首先是转载，地址：http://jaychaoqun.javaeye.com/blog/392110
接下来是理解之后的实例
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<title>简易拖放效果</title>
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<script>
//参考：http://www.javaeye.com/topic/57760
//http://jaychaoqun.javaeye.com/blog/392110
//简化id选择器
var isIE = (document.all) ? true : false;
var $ = function (id) {
return "string" == typeof id ? document.getElementById(id) : id;
};
//初始化一个 Class 对象， 它有一个成员，是一个方法， 这个方法返因另一个方法（方法是对象，所以可以作为参数或者返回值）
var Class = {
create: function() {
return function() { //使用new操作符时，就会在新产生的对象上调用这个方法
this.initialize.apply(this, arguments); //这里就是调用 this 对象上的 initialize方法， 并传递 arguments，这里的this是new之后构造出来的对象
}
}
}
//继承，这里没有用到
var Extend = function(destination, source) {
for (var property in source) {
destination[property] = source[property];
}
}
//参数传递
//object参数，fun方法
var Bind = function(object, fun) {
return function() {
return fun.apply(object, arguments);
}
}
//事件传递
//object参数，fun方法
var BindAsEventListener = function(object, fun) {
return function(event) {
return fun.call(object, (event || window.event));
}
}
//事件绑定
//oTarget绑定目标，sEventType事件类型，fnHandler事件方法
function addEventHandler(oTarget, sEventType, fnHandler) {
if (oTarget.addEventListener) { //FF
oTarget.addEventListener(sEventType, fnHandler, false);
} else if (oTarget.attachEvent) { //IE
oTarget.attachEvent("on" + sEventType, fnHandler);
} else {
oTarget["on" + sEventType] = fnHandler;
}
};
//移除事件绑定
//oTarget绑定目标，sEventType事件类型，fnHandler事件方法
function removeEventHandler(oTarget, sEventType, fnHandler) {
if (oTarget.removeEventListener) { //FF
oTarget.removeEventListener(sEventType, fnHandler, false);
} else if (oTarget.detachEvent) { //IE
oTarget.detachEvent("on" + sEventType, fnHandler);
} else {
oTarget["on" + sEventType] = null;
}
};
//SimpleDrag是一个方法，方法体，这里相当于一个类
var SimpleDrag = Class.create();
SimpleDrag.prototype = {
//对象初始化，实现Class中的this.initialize
initialize: function(drag) {
this.Drag = $(drag); //绑定目标
this._x = this._y = 0; //初始值
this._fnMove = BindAsEventListener(this, this.Move);
this._fnStop = Bind(this, this.Stop);
this.Drag.style.position = "absolute";
addEventHandler(this.Drag, "mousedown", BindAsEventListener(this, this.Start));//监听鼠标按下事件
},
//准备拖动
Start: function(oEvent) {
this._x = oEvent.clientX - this.Drag.offsetLeft;
this._y = oEvent.clientY - this.Drag.offsetTop;
addEventHandler(document, "mousemove", this._fnMove); //对象开始拖动后，监听鼠标移动事件
addEventHandler(document, "mouseup", this._fnStop); //同时监听鼠标放开事件
},
//拖动
Move: function(oEvent) {
this.Drag.style.left = oEvent.clientX - this._x + "px";
this.Drag.style.top = oEvent.clientY - this._y + "px";
},
//停止拖动
Stop: function() {
removeEventHandler(document, "mousemove", this._fnMove);
removeEventHandler(document, "mouseup", this._fnStop);
}
};
</script>
<div id="idDrag" style="border:5px solid #0000FF; background:#C4E3FD; 50px; height:50px;"></div>
<script>
new SimpleDrag("idDrag");
</script>
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