How can I disable a Drupal form submit button when it is clicked to prevent double submission?

$form['submit'] = array(
  '#type' => 'submit',
  '#value' => t('Save'),
  '#attributes' => array(
    'onclick' => 'javascript:var s=this;setTimeout(function(){s.value="Saving...";s.disabled=true;},1);',
  ),
);