drupal_add_js(), script not executed I try to include a simple script (below) and cant get it to work.

(function ($) {
  Drupal.behaviors.myModuleBehavior = function (context) {
    alert('say something pretty please');
  }
})(jQuery);


The script is added within a hook_form_alter function

drupal_add_js(drupal_get_path('module', 'my_module') . '/js/my_module_form.js', 'file');


Up to here, no issues. I see the script is added to the long line of js:extends with the correct path. Thus I would expect to receive an alert... but nothing happens. 

As I've run out of things to check for and consulted docs, google and this site, only to find that the code should work, is anyone able to point out what might be wrong here?
I believe the = function (context) bit needs to include the attach:

(function ($) {
  Drupal.behaviors.myModule = {
    attach: function (context, settings) {
      alert('say something pretty please');
    }
  };
})(jQuery);