Luhn check-digit and validation

luhn.js

String.prototype.toLuhn = function() {   

  var sum = 0
  
  this.replace(/\D+/g,'').replace(/[\d]/g, function(c, p, o){
      sum += [[0, 1, 2, 3, 4, 5, 6, 7, 8, 9], [0, 2, 4, 6, 8, 1, 3, 5, 7, 9]][(o.length-p) & 1][parseInt(c, 10)]
  })
  
  return this + ((10 - sum % 10) % 10)
}

String.prototype.isLuhn = function()
{
    var len = this.length
      , mul = 0
      , sum = 0

    while (len--) {
        sum += [[0, 1, 2, 3, 4, 5, 6, 7, 8, 9], [0, 2, 4, 6, 8, 1, 3, 5, 7, 9]][mul][parseInt(this.charAt(len), 10)]
        mul ^= 1
    }

    return sum % 10 === 0 && sum > 0
}