继承的拖拽

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
    div{
        width: 100px;
        height: 100px;
        position: absolute;
        cursor: pointer;
    }
    #div1{
        top: 0;
        background-color: red;
    }
    #div2{
        top: 200px;
        background-color: green;
    }
    </style>
    <script>
    window.onload = function(){
        new Drag("div1");
        new ChildDrag("div2");

        //var drag1 = new Drag("div1");
        //console.log(drag1.oDiv.onmousedown());
    };
    function Drag(id){
            this.oDiv = document.getElementById(id);
            this.disX = 0;
            this.disY = 0;
            var _this = this;
            this.oDiv.onmousedown = function(ev){
                var oEvent = ev || event;
                _this.mouseDown(oEvent);
                return false;//这个位置很有讲究
            };
    }
    Drag.prototype.mouseDown = function(oEvent){
        this.disX = oEvent.clientX - this.oDiv.offsetLeft;
        this.disY = oEvent.clientY - this.oDiv.offsetTop;
        var _this = this;
        if(this.oDiv.setCapture){
            this.oDiv.onmousemove = function(ev){
                var oEvent = ev || event;
                _this.mouseMove(oEvent);//谁调用属于谁
            };
            this.oDiv.onmouseup = function(){
                _this.mouseUp(this);//this指this.oDiv
            };
            this.oDiv.setCapture();
        }
        else{
            document.onmousemove = function(ev){
                var oEvent = ev || event;
                _this.mouseMove(oEvent);
            };
            document.onmouseup = function(){
                _this.mouseUp(this);//this指document
            };
        }
        //return false;//这个位置很有讲究
    };
    Drag.prototype.mouseMove = function(oEvent){
        var x = oEvent.clientX - this.disX;
        var y = oEvent.clientY - this.disY;
        this.oDiv.style.left = x + "px";
        this.oDiv.style.top = y + "px";
    };
    Drag.prototype.mouseUp = function(obj){
        obj.onmousemove = obj.onmouseup = null;//this指this.oDiv或document
        if(this.oDiv.releaseCapture){
            this.oDiv.releaseCapture();
        }
    };

    function ChildDrag(id){
        Drag.call(this,id);//属性call
    }
    function extend(obj1,obj2){//方法拷贝继承
        for(var attr in obj2){
            obj1[attr] = obj2[attr];
        }
    }
    extend(ChildDrag.prototype,Drag.prototype);
    ChildDrag.prototype.mouseMove = function(oEvent){
        var x = oEvent.clientX - this.disX;
        var y = oEvent.clientY - this.disY;
        if(x < 20){
            x = 0;
        }
        else if(x > document.documentElement.clientWidth - this.oDiv.offsetWidth - 20){
            x = document.documentElement.clientWidth - this.oDiv.offsetWidth;
        }
        if(y < 20){
            y = 0;
        }
        else if(y > document.documentElement.clientHeight - this.oDiv.offsetHeight - 20){
            y = document.documentElement.clientHeight - this.oDiv.offsetHeight;
        }
        this.oDiv.style.left = x + "px";
        this.oDiv.style.top = y + "px";
    };
    </script>
</head>
<body>
    <div id="div1"></div>
    <div id="div2"></div>
</body>
</html>

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原文地址：https://www.cnblogs.com/jiujiaoyangkang/p/5753563.html