How to make form buttons call only javascript?

Question

I'm experimenting with JavaScript and Drupal forms. Currently I'm trying to make a button in the administration form of a module that will use JavaScript to append options to a select list. The problem I'm running into is that when I click the button, my JavaScript gets called but the whole form refresh. I've looked at the Forms API reference thinking there was some kind of attribute I can set on the button to stop it from but found nothing. Is there any way I can stop the button from refreshing the page or is this a dead end?

$form['#attached']['js'] = array(
  drupal_get_path('module', 'test').'/js/test.js',
);

$form['list'] = array(
  '#type' => 'select',
  '#options' => array(),
  '#attributes' => array(
    'name' => 'sellist',
  ),
  '#size' => 4,
);

$form['add_button'] = array(
  '#type' => 'button',
  '#value' => 'Add',
  '#attributes' => array(
    'onclick' => "add_to_list(this.form.sellist, 'Append' + this.form.sellist.length);",
  ),
);

//JavaScript
function add_to_list(list, text) {
  try {
    list.add(new Option(text, list.length), null) //add new option to end of "sample"
  }
  catch(e) {
    list.add(new Option(text, list.length));
  }
}

My final code:

<?php
function jstest_menu() {
  $items['admin/config/content/jstest'] = array(
    'title' => 'JavaScript Test',
      'description' => 'Configuration for Administration Test',
      'page callback' => 'drupal_get_form',
      'page arguments' => array('_jstest_form'),
      'access arguments' => array('access administration pages'),
      'type' => MENU_NORMAL_ITEM,
  );

  return $items;
}

function _jstest_form($form, &$form_state) {
  $form['list'] = array(
    '#type' => 'select',
    '#options' => array(),
    '#size' => 4,
  );

  $form['text'] = array(
    '#type' => 'textfield',
  );

  $form['add_button'] = array (
    '#type' => 'button',
    '#value' => t("Add"),
    '#after_build' => array('_jstest_after_build'),
  );
  return $form;
}

function _jstest_after_build($form, &$form_state) {
  drupal_add_js(drupal_get_path('module', 'jstest').'/js/jstest.js');
  return $form;
}

JavaScript
(function ($) {
  Drupal.behaviors.snmpModule = {
    attach: function (context, settings) {
      $('#edit-add-button', context).click(function () {
        var list = document.getElementById('edit-list');
        var text = document.getElementById('edit-text');

        if (text.value != '')
        {
          try {
            list.add(new Option(text.value, list.length), null);
          }
          catch(e) {
            list.add(new Option(text.value, list.length));
          }

          text.value = '';
        }

        return false;
      });
      $('#edit-list', context).click(function () {
        var list = document.getElementById('edit-list');

        if (list.selectedIndex != -1)
          list.remove(list.selectedIndex);

        return false;
      });
    }
  };
}(jQuery));

Answer 1

The most easy way to accomplish this is just return false in your javascript code:

function add_to_list(list, text) {
  try {
    list.add(new Option(text, list.length), null);
    return false;
  } catch(e) {
    list.add(new Option(text, list.length));   
    return false;
  }
}

or a better way is using behaviors:

Drupal.behaviors.some_action = function(context) {
  $('#id-button:not(.button-processed)',context)
  .addClass('button-processed').each(function() {

    //whatever you want here
    return false;
  });
}

Answer 2

the form button definition below works for me, the #after_build is useful for loading in javascript that can attach the click handler.

$form['add_button'] = array (
  '#type' => 'button',
  '#attributes' => array('onclick' => 'return (false);'),
  '#value' => t("Add"),
);

$form['#after_build'] = array('[module_name]_after_build');

Then my javascript that is loaded in a separate file by the after build function, looks something like:

Drupal.behaviors.[module_name] = function(context) {
  $('#edit-add-button').click(function() {
   ...Do something here
  });
};

Answer 3

You can just add the return false statement after your function call, inside the attribute line of the button form element:

'#attributes' => array(
   'onclick' => "add_to_list(this.form.sellist, 'Append' + this.form.sellist.length); return false",
),

Answer 4

Ideally, have a read into Drupal's own AJAX (or AHAH) form abilities. Really basic intro here http://drupal.org/node/752056

Otherwise, I'm surprised it is refreshing the page as it is just a 'button' not a submit or anything.

Does it need the javascript to return false, like on an link does to stop it jumping back to the top of the page?