js实现让div可拖动

  随着时代的变化，越来越感觉到js的重要性，js不仅可以做web页面(如Ext框架)，还可以做一些web的特效，这些特效不仅兼容PC，而且兼容手机端，毕竟是基于浏览器的，和平台没关系。现在微软的windows8 系统的App都可以用js开发了，大家有时间可以去尝试一下。

       现在切入正题，说一下js 实现可拖动div.实现这个功能我们先说一下思路：

     1.捕捉鼠标div的mousedown事件

     2.捕捉 document的   mousemove事件

      3.取消事件

然后我们看一下代码：

function Drag(id) {
var $ = function (flag) {
return document.getElementById(flag);
}
$(id).onmousedown = function (e) {
var d = document;
var that=this;
var page = {
event: function (evt) {
var ev = evt || window.event;
return ev;
},
pageX: function (evt) {
var e = this.event(evt);
return e.pageX || (e.clientX + document.body.scrollLeft - document.body.clientLeft);
},
pageY: function (evt) {
var e = this.event(evt);
return e.pageY || (e.clientY + document.body.scrollTop - document.body.clientTop);

},
layerX: function (evt) {
var e = this.event(evt);
return e.layerX || e.offsetX;
},
layerY: function (evt) {
var e = this.event(evt);
return e.layerY || e.offsetY;
}
}
var x = page.layerX(e);
var y = page.layerY(e);
if (that.setCapture) {
that.setCapture();
}
else if (window.captureEvents) {
window.captureEvents(Event.MOUSEMOVE | Event.MOUSEUP);
}
d.onmousemove = function (e) {
var tx = page.pageX(e) - x;
var ty = page.pageY(e) - y;
that.style.left = tx + "px";
that.style.top = ty + "px";
}
d.onmouseup = function () {
if (that.releaseCapture) {
that.releaseCapture();
}
else if (window.releaseEvents) {
window.releaseEvents(Event.MOUSEMOVE | Event.MOUSEUP);
}
d.onmousemove = null;
d.onmouseup = null;
}
}
}

代码分析：

 
获取div对象
var $ = function (flag) {

                return document.getElementById(flag);

            }    

捕捉document的mousedown事件：
里面有这么一段代码：
     var page = {

                    event: function (evt) {

                        var ev = evt || window.event;

                        return ev;

                    },

                    pageX: function (evt) {

                        var e = this.event(evt);

                        return e.pageX || (e.clientX + document.body.scrollLeft - document.body.clientLeft);

                    },

                    pageY: function (evt) {

                        var e = this.event(evt);

                        return e.pageY || (e.clientY + document.body.scrollTop - document.body.clientTop);

                    },

                    layerX: function (evt) {

                        var e = this.event(evt);

                        return e.layerX || e.offsetX;

                    },

                    layerY: function (evt) {

                        var e = this.event(evt);

                        return e.layerY || e.offsetY;

                    }

                }
其中event获取鼠标事件，pageX，pageY获取鼠标的坐标，layerX，layerY获取鼠标距离div边框的距离。
还有一段代码：
             if (dv.setCapture) {

                    dv.setCapture();

                }

                else if (window.captureEvents) {

                    window.captureEvents(Event.MOUSEMOVE | Event.MOUSEUP);

                }
这个就是捕捉div的MouseMove和MouseUp事件，不懂得tx可以到网上查查。
 document的MouseMove和mouseUp事件： 

d.onmousemove = function (e) {                    

                    var tx = page.pageX(e) - x;

                    var ty = page.pageY(e) - y;

                    dv.style.left = tx + "px";

                    dv.style.top = ty + "px";

                }   

                d.onmouseup = function () {

                    if (dv.releaseCapture) {

                        dv.releaseCapture();

                    }

                    else if (window.releaseEvents) {

                        window.releaseEvents(Event.MOUSEMOVE | Event.MOUSEUP);

                    }

                    d.onmousemove = null;

                    d.onmouseup = null;

                }

其中的tx,ty就是最重要的代码了，是设置div坐标的

有的人可能会问为什么要-x,-y?

x,y其实就是获取鼠标距离div边框的距离，如果不减掉的话

鼠标箭头的坐标和div的x,y坐标一样了，这样拖动之后，鼠标的位置会偏到左上角，效果就是，拖动之后会弹动一下。

                if (dv.releaseCapture) {

                        dv.releaseCapture();

                    }

                    else if (window.releaseEvents) {

                        window.releaseEvents(Event.MOUSEMOVE | Event.MOUSEUP);

                    }

                    d.onmousemove = null;

                    d.onmouseup = null;

上面这段代码就是在鼠标松开之后取消document的onmousemove，onmouseup事件。

 

 最近都在学习js，后续有新的心得体会也会与大家分享，希望与大家共同学习，进步。
参考：http://www.cnblogs.com/a546558309/p/3476726.html