代码用网上别人的，结果是进去了定时执行代码，可是图片还是旧的，不会定时刷新．

<canvas id="myCanvas" width="472" height="472" style="border:1px solid #c3c3c3;">  Your browser does not support the canvas element. </canvas>  <FONT SIZE=1 id="F1"></FONT> <FONT SIZE=1 id="F2"></FONT>    <script>  var i_height = 472;  var i_width = 472;  var pic = document.getElementById("myCanvas");  pic.style.height = i_height + "px";  pic.style.width = i_width + "px"; </script>  <script type="text/javascript">  var n = 0;  var image = new Image();//放入函数里面：浏览器运行一分钟左右系统内存用到高达 90%，故做一个全局的反冲图片  function changeImage() {   var canvas = document.getElementById("myCanvas");   var cxt = canvas.getContext("2d");   //ctx.restore();   image.src = "/static/wx_login1.jpg";   image.onload = function () //确保图片已经加载完毕   {    n = n + 1;    n = n % 100;    document.getElementById("F1").innerHTML = "刷新:" + n;    if (image.complete)//如果图片加载完成，绘制     cxt.drawImage(image, 0, 0);    else     alert(image.complete);    }   image.onerror = function () {    document.getElementById("F2").innerHTML = "error N:" + n;   };   //ctx.save();  }   setInterval("changeImage();", 2000); </script>