Add jQuery to exposed filter form on drupal 7

Question

I've been searching around how to add jQuery to Drupal 7, but i couldn't make it work. Here is my steps:

Step 1: I create a javascript file and put into my module under js directory.

Step 2: I added the file to my module .info

 scripts[] = js/xxx.js

Step 3: The contents of the xxx.js

(function ($) 
{
  Drupal.behaviors.mymodule =
  {
    attach: function(context, settings) {

    $("#edit-field_a",context).change(function(){
      currentValue = $(this).val();
      alert(currentValue); // no fire at all
      if(currentValue == 'a')
        {
            $('#edit-field_b').val('All');
        }
    }

}
};

})(jQuery);

All the fields are on exposed filter form. I wish to do something like the value of the field_b select list changed based on field_a select list.

What did i miss? Is my jQuery correct?

Updates: Previous js is wrong, corrected here.

 (function ($) 
{
  Drupal.behaviors.mymodule =
  {
    attach: function(context, settings) {

    $("#edit-field_a",context).change(function(){
      currentValue = $(this).val();
      alert(currentValue); // no fire at all
      if(currentValue == 'a')
        {
            $('#edit-field_b').val('All');
        }
    });

}
}

})(jQuery);

Answer 1

Do like this:

function MY_MODULE_form_views_exposed_form_alter(&$form, &$form_state, $form_id) {
  if ($form['#id'] == 'FORM-ID') {
    $form['#attached']['js'] = array(
      drupal_get_path('module', 'MY_MODULE') . '/js/SCRIPT.js' => array(
        'type' => 'file',
        'group' => JS_LIBRARY, // or JS_DEFAULT, JS_THEME.. read this -  https://api.drupal.org/api/drupal/includes!common.inc/function/drupal_add_js/7
      ),
    );
  }
}