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<script>
  
  lp.jQuery(function($) {
  
    var ruleID = 'zipCode'
    var field = 'zip_code';
    var message = 'Please enter a valid ZIP code';
  
    var rules = module.lp.form.data.validationRules[field];
  
    $.validator.addMethod(ruleID, function(value, field) {
      var valid = /^\d{5}([\-]?\d{4})?$/.test(value);
      return valid || (!rules.required && !value);
    }, message);
  
    rules[ruleID] = true;
  
  });

</script>