拖拽功能以及组件的延展

HTML部分

    <div id="div1"></div>
    <div id="div2"></div>

CSS部分

    <style>
        #div1{width: 100px;height: 100px;background-color: red;position: absolute;}
        #div2{width: 100px;height: 100px;background-color: blue;position: absolute;left:100px;}
    </style>

普通JS写法

    //普通写法
   function Drag(id){
        var obj = document.getElementById(id);
        var disX = 0;
        var disY = 0;
        obj.onmousedown = function(ev){
            var ev = ev || window.event;
            disX = ev.clientX - obj.offsetLeft;
            disY = ev.clientY - obj.offsetTop;
            document.onmousemove = function(ev){
                var ev = ev || window.event;
                obj.style.left = ev.clientX - disX + "px";
                obj.style.top = ev.clientY - disY + "px";
            }
            document.onmouseup = function(){
                document.onmouseup = document.onmousemove = null;
            }
        }
    }

    window.onload = function(){
        Drag("div1");
        Drag("div2");
}

面向对象的写法：

    function Drag(id){
        this.obj = document.getElementById(id);
        this.disX = 0;
        this.disY = 0;
    }
    Drag.prototype.init = function(){
        var that = this;
        this.obj.onmousedown = function(ev) {
            var ev = ev || window.event;
            that.fnDown(ev);

            document.onmousemove = function (ev) {
                var ev = ev || window.event;
                that.fnMove(ev);
            }
            document.onmouseup = function () {
                document.onmousemove = null;
                document.onmouseup = null;
            }
        }
        return false;
    }
    Drag.prototype.fnDown = function(ev){
        this.disX = ev.clientX - this.obj.offsetLeft;
        this.disY = ev.clientY - this.obj.offsetTop;
    };
    Drag.prototype.fnMove = function(ev){
        this.obj.style.left = ev.clientX - this.disX + ‘px‘;
        this.obj.style.top = ev.clientY - this.disY + ‘px‘;
    };
　　//继承父类的子组件
    function childDrag(id){
        Drag.call(this,id);
    }　　
    function extend(obj1,obj2){
        for(var attr in obj2) {
            obj1[attr] = obj2[attr];
        }
    }
    extend(childDrag.prototype,Drag.prototype);　　 //重新定义fnMove函数
    childDrag.prototype.fnMove = function(ev){
        var  L = ev.clientX - this.disX;
        var  T = ev.clientY - this.disY;
        if(L<0){
            L = 0;
        }else if(L>document.documentElement.clientWidth - this.obj.offsetWidth){
            L = document.documentElement.clientWidth - this.obj.offsetWidth;
        }
        if(T<0){
            T = 0;
        }else if(T>document.documentElement.clientHeight - this.obj.offsetHeight){
            T = document.documentElement.clientHeight - this.obj.offsetHeight;
        }
        this.obj.style.left = L + ‘px‘;
        this.obj.style.top = T + ‘px‘;
    };

    window.onload = function(){
        var obj = new Drag("div1");
        obj.init();

        var obj2 = new childDrag("div2");
        obj2.init();
    }