JS修改iframe页面背景颜色的方法

<!DOCTYPE html>
<html>
<head>
<script>
function changeStyle()
{
var x=document.getElementById("myframe");
var y=(x.contentWindow || x.contentDocument);
if (y.document)y=y.document;
y.body.style.backgroundColor="#0000ff";
}
</script>
</head>
<body>
<iframe id="myframe" src="demo_iframe.htm">
<p>Your browser does not support iframes.</p>
</iframe>
<br><br>
<input type="button" onclick="changeStyle()" 
value="Change background color">
</body>
</html>