分享一个通过面向对象方式完成的拖拽功能

研究了两天的JS面向对象了，然后根据视频完成了一个简单的拖拽功能。下面的代码其实很简单，唯一需要注意的就是 this ，感觉JS中的this还是很奇妙很有意思的，接下来学习就研究this指针好啦。

下面是拖拽的代码

Drag.js

function Drag(id){

    var _this = this;

    this.divX = 0;
    this.divY = 0;

    this.oDiv = document.getElementById(id);

    this.oDiv.onmousedown = function(ev){
        _this.fnMouseDown(ev);
    }
}

Drag.prototype.fnMouseDown = function(ev){

    var _this = this;

    var oEvent = ev||event;

    this.divX = oEvent.clientX - this.oDiv.offsetLeft;
    this.divY = oEvent.clientY - this.oDiv.offsetTop;

    document.onmousemove = function(ev){
        _this.fnMouseMove(ev);

        return false;//取消选中
    };

    document.onmouseup = function(){
        _this.fnMouseUp();
    }

}

Drag.prototype.fnMouseMove = function(ev){
    var oEvent = ev||event;

    this.oDiv.style.left = oEvent.clientX - this.divX+'px';
    this.oDiv.style.top = oEvent.clientY- this.divY+'px';
}

Drag.prototype.fnMouseUp = function(){
    document.onmousemove = null;
    document.onmousedown = null;
}

LimitDrag.js //限制范围的拖拽

/**
 * Created by Administrator on 2015/12/29 0029.
 */
function LimitDrag (id){
    Drag.call(this,id);
}

for(var i in Drag.prototype){
    LimitDrag.prototype[i] = Drag.prototype[i];
}

//重写 MouseMove 函数

LimitDrag.prototype.fnMouseMove = function(ev){

    var oEvent = ev||event;

    var left = oEvent.clientX - this.divX;
    var top = oEvent.clientY - this.divY

    if(left<0){
        left = 0;
    }else if(left >document.documentElement.clientWidth - this.oDiv.offsetWidth){
        left= document.documentElement.clientWidth - this.oDiv.offsetWidth;
    }

    if(top<0){
        top = 0;
    }else if(top > document.documentElement.clientHeight - this.oDiv.offsetHeight){
        top =  document.documentElement.clientHeight - this.oDiv.offsetHeight
    }

    this.oDiv.style.left = left+'px';
    this.oDiv.style.top = top+'px';

}

HTML

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="js/Drag.js"></script>
    <script src="js/LimitDrag.js"></script>
    <script>

        window.onload = function () {
            new Drag('div1');
            new LimitDrag('div2')
        }

    </script>
    <style>
        #div1{
              200px;
             height: 200px;
             background-color: yellow;
             position: absolute;
         }

        #div2{
             200px;
            height: 200px;
            background-color: blue;
            position: absolute;
        }

    </style>
</head>
<body>

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

</body>
</html>