jquery拖动代码

实现以下目标：

html代码：

<style type="text/css">
.page{text-align:left;}
.dragDiv{border:1px solid #ddd; padding:10px; width:300px; margin:0 auto; border-radius:4px; box-shadow:0 1px 2px #fefefe; position: fixed;}
</style>
<div class="dragDiv" id="drag">
<div class="drag-head">点击拖动</div>
<div class="drag-body">
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</div>
</div>

jQuery代码：

var _drag = {};
_drag.top = 0; //拖动过的位置距离上边
_drag.left = 0; //拖动过的位置距离左边
_drag.maxLeft; //距离左边最大的距离
_drag.maxTop; //距离上边最大的距离
_drag.dragging = false; //是否拖动标志
//拖动函数
function bindDrag(el){
var winWidth = $(window).width(), winHeight =$(window).height(),objWidth = $(el).outerWidth(), objHeight = $(el).outerHeight();
_drag.maxLeft = winWidth - objWidth, _drag.maxTop = winHeight - objHeight;
var els = el.style,x=0,y=0;
var objTop = $(el).offset().top, objLeft = $(el).offset().left;
$(el).mousedown(function(e){
_drag.dragging = true;
_drag.isDragged = true;
x = e.clientX - el.offsetLeft;
y = e.clientY - el.offsetTop;
el.setCapture && el.setCapture();
$(document).bind('mousemove',mouseMove).bind('mouseup',mouseUp);
return false;
});
function mouseMove(e){
e = e || window.event;
if(_drag.dragging){
_drag.top = e.clientY - y;
_drag.left = e.clientX - x;
_drag.top = _drag.top > _drag.maxTop ? _drag.maxTop : _drag.top;
_drag.left = _drag.left > _drag.maxLeft ? _drag.maxLeft : _drag.left;
_drag.top = _drag.top < 0 ? 0 : _drag.top;
_drag.left = _drag.left <0 ? 0 : _drag.left;
els.top = _drag.top + 'px';
els.left = _drag.left+ 'px';
return false;
}

}
function mouseUp(e){
_drag.dragging = false;
el.releaseCapture && el.releaseCapture();
e.cancelBubble = true;
$(document).unbind('mousemove',mouseMove).unbind('mouseup',mouseUp);
}
$(window).resize(function(){
var winWidth = $(window).width(),
winHeight = $(window).height(),
el = $(el),
elWidth = el.outerWidth(),
elHeight = el.outerHeight(),
elLeft = parseFloat(el.css('left')),
elTop = parseFloat(el.css('top'));
_drag.maxLeft = winWidth - elWidth;
_drag.maxTop = winHeight - elHeight;
_drag.top = _drag.maxTop < elTop ? _drag.maxTop : elTop;
_drag.left = _drag.maxLeft < elLeft ? _drag.maxLeft : elLeft;
el.css({
top:_drag.top,
left:_drag.left
})
})
}
bindDrag(document.getElementById('drag'));

演示地址：