Levenshtein distance between two given strings implemented in JavaScript and usable as a Node.js module

levenshtein.js

/*  String.similarTo("compare", [BOOL (default TRUE) if do reverse check])
 *  Credit to for base formula Andrei Mackenzie
 *    https://gist.github.com/andrei-m/982927
 **/
;(function() {
	function l(a, b) {
		if(a.length == 0) return b.length;
		if(b.length == 0) return a.length;
		var matrix = [];
		for(var i=0;i<=b.length;i++) matrix[i] = [i];
		for(var j=0;j<=a.length;j++) matrix[0][j] = j;
		for (var i=1;i<=b.length;i++)
			for (var j=1;j<=a.length;j++)
				b.charAt(i - 1) == a.charAt(j - 1) ? matrix[i][j] = matrix[i - 1][j - 1] : matrix[i][j] = Math.min(matrix[i - 1][j - 1] + 1, Math.min(matrix[i][j - 1] + 1, matrix[i - 1][j] + 1));
		return matrix[b.length][a.length];
	}
	function s(b, x) {
		var a = this.toString(),
			i = l(a, b);
		return x ? i : function() {
			var	r = function (a){a=a.split("");for(var c=[],b=a.length-1;0<=b;b--)c.push(a[b]);return c.join("")};
				c = r(b),
				j = l(a, c);
			return i < j ? i : j;
		}();
	}
	if (Object['defineProperty'] && !String.prototype.hasOwnProperty('similarTo')) Object.defineProperty(String.prototype, 'similarTo', { value: s });
})();