Validate a barcode UPC-E, UPC-A, EAN, EAN-14, SSCC

validate_barcode.js

// checksum calculation for GTIN-8, GTIN-12, GTIN-13, GTIN-14, and SSCC
// based on http://www.gs1.org/barcodes/support/check_digit_calculator
function isValidBarcode(barcode) {
  // check length
  if (barcode.length < 8 || barcode.length > 18 ||
      (barcode.length != 8 && barcode.length != 12 &&
      barcode.length != 13 && barcode.length != 14 &&
      barcode.length != 18)) {
    return false;
  }

  var lastDigit = Number(barcode.substring(barcode.length - 1));
  var checkSum = 0;
  if (isNaN(lastDigit)) { return false; } // not a valid upc/ean

  var arr = barcode.substring(0,barcode.length - 1).split("").reverse();
  var oddTotal = 0, evenTotal = 0;

  for (var i=0; i<arr.length; i++) {
    if (isNaN(arr[i])) { return false; } // can't be a valid upc/ean we're checking for

    if (i % 2 == 0) { oddTotal += Number(arr[i]) * 3; }
    else { evenTotal += Number(arr[i]); }
  }
  checkSum = (10 - ((evenTotal + oddTotal) % 10)) % 10;

  // true if they are equal
  return checkSum == lastDigit;
}

validate_barcode_function.rb

def valid_upc(upc)
  # check length
  if (upc.length < 8 or upc.length > 18 or
       (upc.length != 8 && upc.length != 12 &&
        upc.length != 13 && upc.length != 14 &&
        upc.length != 18)
     )
    return false
  end

  last_digit = upc.slice!(-1).to_i
  check_sum = 0

  arr = upc.split(//).reverse
  odd_total = even_total = 0

  arr.each_index do |i|
    if (i % 2 == 0)
      odd_total = odd_total + (arr[i].to_i * 3)
    else
      even_total = even_total + arr[i].to_i
    end
  end
  check_sum = (10 - ((even_total + odd_total) % 10)) % 10

  # true if they are equal
  return check_sum == last_digit
end

The JS version does not have barcode.length != 12 at the beginning.

that only applies for a generic UPC an EAN is 13, so no the suggestion is not valid