Example of using regex with Javascript.

regex.js

// Validate IMEI numbers.
$('#RequestProofOfPurchaseFloorStockForm').find('.imei').each(function() {
  var pattern = /^(?!\b(.)\1+\b)\d{15}$/gi;
  if(pattern.test($(this).val()) == false) {
      validate = false;
      $(this).addClass('err');
      $(this).parent().find('label').addClass('err');
  }
});