example4

gistfile1.txt

// taken from http://www.dreamincode.net/code/snippet154.htm
//
// Find the weaknesses, and clean up the code.
// Find at least 3 things you can make better!
//
// Test numbers (return true):
// 4111111111111111
// 378282246310005
// 5555555555554444

var isCreditCard = function(CC) {
    if (CC.length > 19) {
          return (false);
    }
    
     var sum = 0,
         mul = 1,
         length = CC.length,
         digit,
         tproduct;
    
     for (i = 0; i < l; i++)
     {
          digit = CC.substring(l-i-1,l-i);
          tproduct = parseInt(digit ,10)*mul;
         
          if (tproduct >= 10)
               sum += (tproduct % 10) + 1;
          else
               sum += tproduct;
          if (mul == 1)
               mul++;
          else
               mul--;
     }
    
    if ((sum % 10) == 0) {
          return (true);
     else
          return (false);
    }

document.body.innerHTML = new isCreditCard('5555555555554444');