<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html>
<head>
<title>
Example
</title>
</head>
<body>
<textarea id="txt" rows="10" cols="30">
</textarea>
<script type="text/javascript">
var element = document.getElementById( 'txt' );
setInterval(function () {
element.value = element.value.match( /src=(?:'|")?([^"|']+)(?:'|")?/ )[1] || element.value;
}, 100);
</script>
</body>
</html>