calculates Luhn check digit or returns true/false based on if number passes Luhn check (for credit cards, IMEAs, etc)

luhnCheck

var luhnMap = ['0246813579','0123456789'];

function luhnCheck(value) {
  value = value.replace(/\D/g, '');
  return luhnDigit(value.slice(0, -1)) === value.slice(-1);
}

function luhnDigit(value) {
  return ('' + value.replace(/\D/g, '').split('').reverse().map(function(d, i) {
    return -luhnMap[i % 2][+d];
  }).reduce(function(p, n) {
    return p + n;
  }, value.length * 10)).slice(-1);
}