用js控制div跟随鼠标移动，鼠标点击后，鼠标离开，div留在当前点击的位置怎么做

var drag_ = false
var D = new Function('obj', 'return document.getElementById(obj);')
var oevent = new Function('e', 'if (!e) e = window.event;return e')
function Move_obj(obj) {
var x, y;
D(obj).onmousedown = function (e) {
drag_ = true;
with (this) {
style.position = "absolute"; var temp1 = offsetLeft; var temp2 = offsetTop;
x = oevent(e).clientX; y = oevent(e).clientY;
document.onmousemove = function (e) {
if (!drag_) return false;
with (this) {
style.left = temp1 + oevent(e).clientX - x + "px";
style.top = temp2 + oevent(e).clientY - y + "px";
}
}
}
document.onmouseup = new Function("drag_=false");
}
}

	
		
		
		
			#box{
				width: 100px;
				height: 100px;
				background-color: skyblue;
				position: absolute;
			}
		
		
			window.onload = function(){
				
				var box = document.getElementById("box");
				
				var move = function(event){
					var x = event.pageX;
					var y = event.pageY;
				
					box.style.left = x - 0.5*box.offsetWidth + "px";
					box.style.top = y - 0.5*box.offsetHeight + "px";
					
				}
				
				box.onclick = function(){
					document.onmousemove = null;
				}
				
				box.ondblclick = function(){
					document.onmousemove = move;
				}
			
				document.onmousemove = move;
			}