return iframe src value in alertbox while it getting attempt to load using javascript

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Javascript

jQuery

but it return empty alert box.. pls anyone help me. I need alertbox with detail of iframe src(address location, http://www.google.com) value.

<iframe width="700px" height="900px" name="ifrm" id="ifrm" onload="load()"></iframe> 

<script type="text/javascript">
function load()
{
var oIframe = document.getElementById("ifrm");

var oDoc = oIframe.contentWindow || oIframe.contentDocument;

if (oDoc.document) {

    oDoc = oDoc.document;
}
alert(oDoc.ifrm.href);
}
</script>