JS-Iframe返回的内容

<!DOCTYPE html>
<html>
<head>
    <title>DOM Level 2 IFrame Example</title>
</head>
<body>
    <iframe id="myIframe" src="javascript:false"></iframe>
    <script type="text/javascript">
        var iframe = document.getElementById("myIframe");
        var iframeDoc = iframe.contentDocument || iframe.contentWindow.document;
        alert(iframeDoc);
    </script>
</body>
</html>