JavaScript format number based on pattern

formatNumber.js

function formatNumber(numbers, pattern){

	//var pattern = '(999) 999-9999';
	var patternArray = pattern.split('').map(function(x) { return isNumber(x) ? null : x; });
	var resultArray = [];

	var pos = 0;

	for (var i = 0; i < patternArray.length; i++) {
		if (patternArray[i] === null) {
			patternArray[i] = numbers[pos];
			pos++;
		}
	}

	return patternArray.join('');

}

function isNumber(n) {
	return n - parseFloat(n) + 1 >= 0;
}