Instead of sending debug data to a log file, just display it in the browser console with the following PHP snippet.

debug-to-console.php

<?php
/**
 * Send debug code to the Javascript console
 */ 
function debug_to_console($data) {
    if(is_array($data) || is_object($data))
	{
		echo("<script>console.log('PHP: ".json_encode($data)."');</script>");
	} else {
		echo("<script>console.log('PHP: ".$data."');</script>");
	}
}
?>