canvas绘制跑马灯lineDashOffset、lineDashOffset

	var canvas = document.getElementById('canvas');
		canvas.width='300';
		canvas.height='300';
		var ctx = canvas.getContext('2d');
		var offset=0;
		
		function draw(){
			ctx.clearRect(0,0, canvas.width, canvas.height);
			ctx.setLineDash([10,4, 2]);//实线和空白的比例
  	   		ctx.lineDashOffset = -offset;//如果是正数则逆时针
       		ctx.strokeRect(100,100, 100, 100);//绘制一个正方形
		}
		function go(){
			offset++;
			draw();
			//延时执行
			setTimeout(go,30)
		}
		
		go();

效果如下：