A simple js validator for CPF /CNPJ

validateCpfCnpj.js

function validateCpfCnpj(cpfCnpj) {

	'use strict';
	
	var arr;
	
	function buildDigit(arr) {

	    var isCpf = arr.length < 11,
	        digit = arr.map(function (val, idx) {return val * ((!isCpf ? idx % 8 : idx) + 2)}).reduce(function (total, current) {return total + current}) % 11;
	
        if (digit < 2 && isCpf) return 0;

        return 11 - digit;
	};
	
	cpfCnpj = cpfCnpj.replace(/\D/g, '');

	if ([11, 14].indexOf(cpfCnpj.length) < 0) return false;
	
	arr = cpfCnpj.split('').reverse().slice(2);

	arr.unshift(buildDigit(arr));
	arr.unshift(buildDigit(arr));

	return cpfCnpj === arr.reverse().join('');

};

I tried it out for the following use case:
CNPJ8 + BranchNumber + XX
While the idea was to find XX using the script above.
In some 65% cases it works. For remaining 33% it does not return any number.
Example CNPJ that it claims to be wrong but that are in fact possible:
12481307000130