Check Digit GS1

checkDigitGS1.js

/*
  Check digit GS1
  Arguments:
    - [String] GS1 code without check digit to generate
      the check digit
  Returns:
    - [Number] Check digit for given code
  
  Author: Matheus R. Kautzmann
*/
var checkDigitGS1 = function(n) {
  var l = n.length, i = 0, v = 0, p = false;

  for(i = l-1; i >= 0; i--) {
    if((p = !p))
      v += (parseInt(n[i], 10) * 3);
    else
      v += parseInt(n[i], 10);
  }

  return ((Math.ceil(v/10) * 10) - v);

};