js 实现鼠标按下 拖动div

	//div 拖动 div的ID
		container.onmousedown = function() {
			//获取鼠标当前坐标 
			var pageX = event.clientX;
			var pageY = event.clientY;
			//获取block的坐标，左边界和上边界 
			var offX = parseInt(this.style.left) || 0;
			var offY = parseInt(this.style.top) || 0;
			//计算出鼠标坐标相对于block坐标的间距 
			var offLX = pageX - offX;
			var offLY = pageY - offY;
			if (!document.onmousemove) {
				document.onmousemove = function() {
					container.style.left = event.clientX - offLX; //设置block的X坐标 
					container.style.top = event.clientY - offLY; //设置block的Y坐标 
				}
			}
		}
		document.onmouseup = function() {
			document.onmousemove = null;
		} //鼠标弹起 
		
		//div 拖动