Comparing lastmodified dates of external files...any ideas?

I'm having trouble figuring out how to compare last modified dates of an external file in javascript.

What i'm trying to accomplish is this:

0. nondescript php code executed here...
1. wait (random 120-240 secs)
2. copy lastmodified_date to old_lastmodified_date.
3. check last modified date of projectvibe.net/pvsamsite/songChange.txt
4. if last_modified_date > old_lastmodified_date then refresh page, otherwise repeat step 1.

I got as far as capturing the last modified date of the external file but that's it. Can someone please help me? Thanks!


<html>

<head>

<title>Last Modified</title>

<script type="text/javascript">

function getLastMod(){

var doc;

var myFrm = document.getElementById('myIframe');

var doc;


if ((doc = myFrm.contentDocument)

|| (myFrm.contentWindow && (doc = myFrm.contentWindow.document))) {

/* ... */

}

var lastModif = new Date(myFrm.contentWindow.document.lastModified);

document.getElementById('LastModified').innerHTML = "Prices correct as at: " + lastModif.toLocaleString();

}

</script>

</head>

<body>

<span id="LastModified"></span>


<iframe id="myIframe" onload="getLastMod()" src="projectvibe.net/pvsamsite/songChange.txt" style="display:none;">

</iframe>


<span id="LastModified"></span>

</body>

</html>