JavaScript 拖放效果

一个可拖放的ＪＳ效果;
 var isIE = (document.all) ? true : false;
var $ = function (id) {
return "string" == typeof id ? document.getElementById(id) : id;
};
var Class = {
create: function() {
return function() { this.initialize.apply(this, arguments); }
}
}
var Extend = function(destination, source) {
for (var property in source) {
destination[property] = source[property];
}
}
var Bind = function(object, fun) {
return function() {
return fun.apply(object, arguments);
}
}
var BindAsEventListener = function(object, fun) {
return function(event) {
return fun.call(object, (event || window.event));
}
}
var CurrentStyle = function(element){
return element.currentStyle || document.defaultView.getComputedStyle(element, null);
}
function addEventHandler(oTarget, sEventType, fnHandler) {
if (oTarget.addEventListener) {
oTarget.addEventListener(sEventType, fnHandler, false);
} else if (oTarget.attachEvent) {
oTarget.attachEvent("on" + sEventType, fnHandler);
} else {
oTarget["on" + sEventType] = fnHandler;
}
};
function removeEventHandler(oTarget, sEventType, fnHandler) {
if (oTarget.removeEventListener) {
oTarget.removeEventListener(sEventType, fnHandler, false);
} else if (oTarget.detachEvent) {
oTarget.detachEvent("on" + sEventType, fnHandler);
} else {
oTarget["on" + sEventType] = null;
}
};
//拖放程序
var Drag = Class.create();
Drag.prototype = {
//拖放对象
initialize: function(drag, options) {
this.Drag = $(drag);//拖放对象
this._x = this._y = 0;//记录鼠标相对拖放对象的位置
this._marginLeft = this._marginTop = 0;//记录margin
//事件对象(用于绑定移除事件)
this._fM = BindAsEventListener(this, this.Move);
this._fS = Bind(this, this.Stop);

this.SetOptions(options);

this.Limit = !!this.options.Limit;
this.mxLeft = parseInt(this.options.mxLeft);
this.mxRight = parseInt(this.options.mxRight);
this.mxTop = parseInt(this.option