Escape php string to javascript string

gistfile1.php

<?php 

/**
* Escape php string to javascript string
* @param string $str
* @return string escaped string
*/
function escape_javascript_string($str){
	// if php supports json_encode, use it (support utf-8)
	if (function_exists('json_encode')) {
		return json_encode($str);
	}
	// php 5.1 or lower not support json_encode, so use str_replace and addcslashes
	// remove carriage return
	$str = str_replace("\r", '', (string) $str);
	// escape all characters with ASCII code between 0 and 31
	$str = addcslashes($str, "\0..\37'\\");
	// escape double quotes
	$str = str_replace('"', '\"', $str);
	// replace \n with double quotes
	$str = str_replace("\n", '\n', $str); 
	return "'{$str}'";
}

$test_case = array(
	'',
	"https://demo/path/download.html?q=query",
	"~!@#$%^&*(){}[]`/=?+\|-_;:'\,<.>",
	'These are the problems => . \ \' \\ \\\\ \\\\\\ \\\\\\\\ "',
	);
foreach ($test_case as $test_str) {
	print '<script>';
	print 'alert(' . escape_javascript_string($test_str) . ')';
	print '</script>';
}