js实现鼠标拖拽效果

$("#box").mousedown(function(e){
	var x = e.offsetX;
	var y = e.offsetY;
	console.log(x,y);
	$(document).mousemove(function(e){
		var _x = e.clientX-x;
		var _y = e.clientY-y;
		console.log(_x,_y);
		$("#box").css({"left":_x,"top":_y});
	})
	$(document).mouseup(function(){
		$(document).unbind("mousemove");
		$(document).unbind("mouseup");
	})
})