Biotoxsin,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script>
$(function() {
$.fn.plugin = function() {
var selector = this.selector;
alert(selector);
//document.querySelector(selector).offsetWidth
}
$('.test').plugin()
});
</script>
</head>
<body>
</body>
</html>