js判读浏览器是否支持html5的canvas的代码

<canvas id="myCanvas" width=”300” height=”200” style="border:1px solid #c3c3c3;"> 
Your browser does not support the canvas element. 
</canvas> 
<script type="text/javascript"> 
var myCanvas = document.getElementById("myCanvas"); 
if (!myCanvas.getContext) 
{ 
alert("你的浏览器不支持Canvas."); 
} 
else 
{ 
alert("你的浏览器支持Canvas."); 
} 
</script>