National Insurance Number generator

generateNINO.js

function generateNINO(style) {
  var group1 = '';
  var group2 = '';
  var group3 = '';
  var group4 = '';
  var group5 = '';
  var randomArrayIndex = '';
  var notAllowed = new Array('GB', 'BG', 'NK', 'KN', 'TN', 'NT', 'ZZ');
  var firstAllowed = new Array('A', 'B', 'C', 'E', 'G', 'H', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'R', 'S', 'T', 'W', 'X', 'Y', 'Z');
  var secondAllowed = new Array('A', 'B', 'C', 'E', 'G', 'H', 'J', 'K', 'L', 'M', 'N', 'P', 'R', 'S', 'T', 'W', 'X', 'Y', 'Z');
  var lastAllowed = new Array('A', 'B', 'C', 'D', '');
  var style = (style == null) ? 1 : style;
  if (style < 1 || style > 2) {
    style = 1;
  }
  while (group1 == '' || notAllowed.indexOf(group1) > -1) {
    randomArrayIndex = Math.floor(Math.random() * firstAllowed.length);
    group1 = firstAllowed[randomArrayIndex];
    randomArrayIndex = Math.floor(Math.random() * secondAllowed.length);
    group1 = group1 + secondAllowed[randomArrayIndex];
  }
  group2 = '' + Math.floor(Math.random() * 10) + Math.floor(Math.random() * 10);
  group3 = '' + Math.floor(Math.random() * 10) + Math.floor(Math.random() * 10);
  group4 = '' + Math.floor(Math.random() * 10) + Math.floor(Math.random() * 10);
  randomArrayIndex = Math.floor(Math.random() * lastAllowed.length);
  group5 = lastAllowed[randomArrayIndex];
  if (style == 1) {
    var final = group1 + group2 + group3 + group4 + group5;
  } else {
    var final = group1 + " " + group2 + " " + group3 + " " + group4;
    if (group5 != '') {
      final = final + " " + group5;
    }
  }
  return final;
}