Luhn Credit Card Validation algorithm implemented as CommonJS module

app.js

/*jslint maxerr:1000 */
var my = {tools:{}};
//Import our module into our project
my.tools.cardHelper = require('credit_card_helper');
//Our test credit card number that we got from http://www.getcreditcardnumbers.com/
var testCreditCardNumber ="49713268648235453";
//Call our verify method to check if our credit card number is in a correct format
var ccCheck = my.tools.cardHelper.verifyCardWithLuhn(testCreditCardNumber);
//alert the result back to the user
alert(ccCheck);

credit_card_helper.js

/*jslint maxerr:1000 */

exports.verifyCardWithLuhn=function(cardNumber){
  //Remove spaces
	cardNumber = cardNumber.replace(/[^\d]/g, "");
	//Grab our length for use later
	var cardLength = cardNumber.length;
	//If no length return invalid 	
	if (cardLength === 0){
		return false;
	}	
	//Get last digit
    var lastDigit = parseInt(cardNumber.substring((cardLength-1),cardLength),10);
    //Build string with all credit card digits minus the last one
    var cardNumberMinusLastDigit = cardNumber.substring(0,(cardLength-1));
    //Build up our variables needed for our calculation
    var sum = 0, luhnLength = cardNumberMinusLastDigit.length, luhnKey = [0,1,2,3,4,-4,-3,-2,-1,0];
  
    //Step 1 of our hash add the numbers together
    for (i=0; i<luhnLength; i++ ) {
      sum += parseInt(cardNumberMinusLastDigit.substring(i,i+1),10);
    }
    //Step 2 of our has, we now add in our key values
    for (i=luhnLength-1; i>=0; i-=2 ) {      
  	  sum += luhnKey[parseInt(cardNumberMinusLastDigit.substring(i,i+1),10)]
    } 
    
    //Adjust our sum as neeed
   	var mod10 = sum % 10;
   	mod10 = 10 - mod10; 
   	if (mod10===10) {      
    	mod10=0;
   	}
    
    //Our hash should now mast the last digit of our number
  	return (mod10===lastDigit);
};