Validate Credit Card (Luhn Algorithm)

cc_validator.js

// http://en.wikipedia.org/wiki/Luhn_algorithm

var _ = require('lodash');

var cc = '7992739871';


function computeChecksum(cc) {
  return _.reduce(cc, function (memo, value, index) {
    var value = parseInt(value, 10);
    if (index % 2 == 1) {
      value = value * 2,
      value =  _.reduce(value.toString().split(''), function (memo, num) {
        return num + memo;
      });
    }
    return value + memo;
  });
}

var checkDigit = (computeChecksum(cc.split('').reverse()) * 9) % 10;

if (checkDigit == 0) {
  console.log('CC is valid');
}
else {
  console.log('CC is invalid');
}