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>