How to add onBlur attribute to ZIP code field in Address Field

In order to control the input format in the ZIP code field in the dynamic address fields provided by the Address Field module (I use it in Drupal Commerce) I need to add the attributes onKeyUp and onBlur to this field. My plan is to use Javascript to manage the formatting, but I need to add the above attributes first. How do I do that? I imagine I should use hook_form_alter in my template.php, but I could need a pointer on how to do it.

if($form['#id'] === "edit-customer-profile-billing-commerce-customer-address-und-0-postal-code"){
  dsm($form); // devel message does not show up in the checkout page in question
  $form['#attributes']['onBlur'] = '(this)'; 
}

EDITED: I have now managed to add the attributes this way:

  function mytheme_form_alter(&$form, &$form_state, $form_id) {
    if($form_id === "commerce_checkout_form_checkout"){
      // Merge new attributes with existing ones.
      $form['customer_profile_billing']['commerce_customer_address']['und']['0']['locality_block']['postal_code']['#attributes'] = array(
        'onBlur' => 'setZip(this)',
        'onKeyUp' => 'setLimit(this,5)',
      );
      $form['customer_profile_shipping']['commerce_customer_address']['und']['0']['locality_block']['postal_code']['#attributes'] = array(
        'onBlur' => 'setZip(this)',
        'onKeyUp' => 'setLimit(this,5)',
      );
    }
  }

And this is the js script (I found it here):

(function($) {
        $(document).ready(function(){
            'use strict';
        var setZip, setLimit;
        console.log('outside');

        function setZip(theField){
          console.log('setzip');
          var num = theField.value.replace(/D/g,"");
          theField.value = num.substr(0,3)+" "+num.substr(2);
        }

        function setLimit(theField, maxDigit){
          console.log('setlimit');
          var num = theField.value.replace(/D/g,"");
          if(num>maxDigit){
            theField.value = theField.value.substr(0,maxDigit);
          }
        }

    });

})(jQuery);

The problem now is that I get a javascript reference error like this:

Uncaught ReferenceError: setZip is not defined at
HTMLInputElement.onblur

I suspect this has something to do with the scope, so I have tried to place the js script with the setLimit and setZip functions in the header, in the body and in the footer, with the same error message. I also tried to remove the $(document).ready(function()… but the reference error reamins.

Any ideas?

  if($("#edit-customer-profile-billing-commerce-customer-address-und-0-postal-code").length){
    document.getElementById("edit-customer-profile-billing-commerce-customer-address-und-0-postal-code").addEventListener("blur", function(){
        if(this.value.length>5 && /s/.test(this.value)){
          this.value = this.value.substr(0,6);
        }   else if(this.value.length>5 && !(/s/.test(this.value))){
                        this.value = this.value.substr(0,5);
                    }
        if(this.value.length===5 && this.value.substring(3,4) !== " "){
            this.value = this.value.split(/(?=.{2}$)/).join(' ');
        }
    });
}