Functions to get filetime in PHP and Javasript

get_filetime.php

<?php
	$fileName = get_template_directory() . '/css/theme.css';
	$modifiedDate = filemtime($fileName);
	echo '<script>console.log(' . $modifiedDate . ')</script>';
?>
<script>
	var fileName = "<?=home_url()?>/wp-content/themes/jims-aircon/css/theme.css";
	var req = new XMLHttpRequest();
	req.open("HEAD", fileName, false);
	req.send(null);
	var modifiedDate = req.getResponseHeader('Last-Modified');
	modifiedDate = Date.parse(modifiedDate) / 1000;
	console.log(modifiedDate);
</script>