JavaScript: preg_replace

preg_replace.js

/**
 * preg_replace (from PHP) in JavaScript!
 *
 * This is basically a pattern replace. You can use a regex pattern to search and 
 * another for the replace. For more information see the PHP docs on the original 
 * function (http://php.net/manual/en/function.preg-replace.php), and for more on 
 * JavaScript flavour regex visit http://www.regular-expressions.info/javascript.html
 *
 * NOTE: Unlike the PHP version, this function only deals with string inputs. No arrays.
 *
 * @author	William Duyck <fuzzyfox0@gmail.com>
 * @license http://www.mozilla.org/MPL/2.0/ Mozilla Public License 2.0
 * 
 * @param	{String}	pattern	The pattern to search for.
 * @param	{String}	replace	The string to replace.
 * @param	{String}	subject	The string to search and replace.
 * @param	{Integer}	limit	The maximum possible replacements.
 * @return	{String}	If matches are found, the new subject will be returned.
 */
var preg_replace = function(pattern, replace, subject, limit){
	if(limit === undefined) {
		limit = -1;
	}

	var _flag		= pattern.substr(pattern.lastIndexOf(pattern[0])+1),
		_pattern	= pattern.substr(1, pattern.lastIndexOf(pattern[0])-1),
		reg	= new RegExp(_pattern, _flag),
		rs	= null,
		res	= [],
		x	= 0,
		y	= 0,
		rtn	= subject;

	var tmp = [];
	if(limit === -1){
		do {
			tmp = reg.exec(subject);
			if(tmp !== null) {
				res.push(tmp);
			}
		} while(tmp !== null && _flag.indexOf('g') !== -1);
	}
	else {
		res.push(reg.exec(subject));
	}
	for(x = res.length -1; x > -1; x--){
		tmp = replace;

		for(y = res[x].length; y > -1; y--){
			tmp = tmp.replace('${' + y + '}', res[x][y])
				.replace('$' + y, res[x][y])
				.replace('\\' + y, res[x][y]);
		}
		rtn = rtn.replace(res[x][0], tmp);
	}
	return rtn;
};