<!DOCTYPE HTML>
<html>
<body>
<canvas id="myCanvas" width="200" height="100" style="border:1px solid #c3c3c3;">
Your browser does not support the canvas element.
</canvas>
<script type="text/javascript">
var c=document.getElementById("myCanvas");
var cxt=c.getContext("2d");
cxt.moveTo(10,10);
cxt.lineTo(10,50);
var dddd=50;
cxt.lineTo(50,50);
cxt.stroke();
ss();
function ss(){
dddd=dddd+1;
cxt.lineTo(dddd,50);
cxt.stroke();
var t1=setTimeout(ss,1);
}
</script>
原文：http://www.cnblogs.com/liuwenbohhh/p/4485608.html