JavaScript面向对象的程序开发之拖拽Demo讲解——xyp_hfwindow.var oDiv = docume

<!DOCTYPE html>
<html lang="en">
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>面向对象的拖拽</title>
<style>
#div1{width:100px;height:100px;background:red;position:absolute;}
</style>
<script type="text/javascript">
/*
    //先用普通方式写个拖拽
    window.onload = function(){
        var oDiv = document.getElementById('div1');
        var disX = 0;
        var disY = 0;
        oDiv.onmousedown = function(){
            var ev = ev || window.event;
            disX = ev.clientX - oDiv.offsetLeft;
            disY = ev.clientY - oDiv.offsetTop;
            document.onmousemove = function(ev){
                var ev = ev || event;
                oDiv.style.left = ev.clientX - disX + 'px';
                oDiv.style.top = ev.clientY - disY + 'px';
            };
            document.onmouseup = function(){
                document.onmousemove = null;
                document.onmouseup = null;
            }
            return false;
        };
    }
*/

/*
    // 再变型  
    var oDiv = null;
    var disX = 0;
    var disY = 0;
    window.onload = function(){
        //3、提取全局变量
        oDiv = document.getElementById('div1');
        //4、将onload中非赋值语句放到初始化函数当中,并在此调用
        init();
    }
    function init(){
        //1、取消函数嵌套函数,将此处的函数拿出去
        oDiv.onmousedown = fnDown;
    }
    function fnDown(){
        var ev = ev || window.event;
        disX = ev.clientX - oDiv.offsetLeft;
        disY = ev.clientY - oDiv.offsetTop;
        //2、取消函数嵌套函数,将此处的函数拿出去,在此处调用
        document.onmousemove = fnMove;
        document.onmouseup = fnUp;
        return false;
    }
    function fnMove(ev){
        var ev = ev || event;
        oDiv.style.left = ev.clientX - disX + 'px';
        oDiv.style.top = ev.clientY - disY + 'px';
    }
    function fnUp(){
        document.onmousemove = null;
        document.onmouseup = null;
    }
*/

//再写成面向对象的方式
window.onload = function(){
    var d1 = new Drag('div1');
    d1.init();
};

function Drag(id){
    this.oDiv = document.getElementById(id);
    this.disX = 0;
    this.disY = 0;
}

Drag.prototype.init = function(){
    var This = this;
    this.oDiv.onmousedown = function(ev){
        var ev = ev || window.event;
        This.fnDown(ev);
        return false;
    };
};

Drag.prototype.fnDown = function(ev){
    var This = this;
    this.disX = ev.clientX - this.oDiv.offsetLeft;
    this.disY = ev.clientY - this.oDiv.offsetTop;
    document.onmousemove = function(ev){
        var ev = ev || event;
        This.fnMove(ev);
    };
    document.onmouseup = this.fnUp;
};
Drag.prototype.fnMove = function(ev){
    this.oDiv.style.left = ev.clientX - this.disX + 'px';
    this.oDiv.style.top = ev.clientY - this.disY + 'px';
};
Drag.prototype.fnUp = function(){
    document.onmousemove = null;
    document.onmouseup = null;
};
</script>
</head>
<body>
    <div id="div1"></div>
</body>
</html>