Settings app is a single place that

  • Allows the user to configure device settings
  • Responds to incoming activities ('configure'), which allows the user to navigate to a specific panel to configure from another app (eg. show the wifi settings panel if no data connection is available).

For new settings key that will be used in system, please do the key migration in apps/system/js/migrators/settings_migrator.js.

Current Status

We are in the middle of the refactoring that targets on the following problem.

The Problem

Currently basic settings services (mozSettings/UI bindings, panel navigation...) used across the app and root panel specific logic are defined together in a few modules (Settings, Connectivity). There are also cases that multiple panels are supported by a single script. These prevent settings app from being launched with only the required scripts and also imapct the perfrmance of loading panels.

The Goal

The goal is to ensure that each panel loads only the required scripts. This could be done by breaking existing modules into smaller and reusable ones. Meanwhile, large scripts should also be splited into modules. By doing this we could achieve:

  1. Module separation
  2. Panel separation
  3. Inline activities
  4. View/logic separation



We are using AMD modules, loaded using 'Alemeda' (a lighter version of RequireJS) and building/optimizing using 'r.js' (the RequireJS optimizer). We have dependencies on files (shared/js) which aren't AMD modules. For those we use the 'shim' options in our requirejs_config.js

Module should not aware the existence of any UI elements, it should only expose the general functionalities that used by panels.

A few fundamental modules are listed below:


SettingsService provides a navigate function for panel navigation. It gets the corresponding panel module from PanelCache and call to its show and hide functions when navigating (see the module/panel.js section).


PanelCache loads panel modules based on panel IDs and caches the loaded modules. If there is no corresponding panel module, it returns SettingsPanel.


Panel is the base object of the panels in settings app. It defines six basic functions: show, hide, beforeShow, beforeHide, init, and uninit. These functions are called by SettingsService during the navigation.

  • init: called at the first time when the beforeShow function gets called
  • uninit: called when cleanup
  • beforeShow: called when the panel is about to be navigated into the viewport
  • beforeHide: called when the panel is about to be navigated out of the viewport
  • show: called when the panel is navigated into the viewport
  • hide: called when the panel is navigated out of the viewport

The internal functions, _onInit, _onBeforeShow, _onShow, _onBeforeHide, _onHide, and _onUninit, are called respectively in the basic functions. The syntax of the functions are:

function _onInit(panelElement [, initOptions])
function _onBeforeShow(panelElement [, beforeShowOptions])
function _onShow(panelElement [, showOptions])
function _onBeforeHide()
function _onHide()
function _onUninit()

We are able to override the internal functions by passing an option object into the constructor of Panel. For example,

  onInit: function(panelElement, initOptions) { //... },
  onBeforeShow: function(panelElement, beforeShowOptions) { //... },
  onShow: function(panelElement, showOptions) { //... },
  onBeforeHide: function() { //... },
  onHide: function() { //... },
  onUninit: function() { //... }

Typically we can create DOM element references in onInit, update UI elements and add listeners in onShow or onBeforeShow, remove listeners in onHide, and do the cleanup in onUninit. The difference between onShow and onBeforeShow is that onBeforeShow is called before the transition, which makes updating the UI before displaying it to users possible.

Note that the transition happens right after onBeforeShow, please avoid heavy things in onBeforeShow and onBeforeHide, or it may drag down the performance of the transition.


SettingsPanel extends Panel with basic settings services. It presets the UI elements based on the values in mozSettings and add listeners responding to mozSettings changes in onBeforeShow. In onInit it parses the panel element for activating links. It also removes listeners in onHide so that we can avoid unwanted UI updates when the panel is outside of the viewport.

As we are using require.js for module management, scripts used in a panel should be wrapped in an AMD module or loaded from it, and which should extends from SettingsPanel to have basic settings services. Similar to Panel, we are able override onShow, onHide, onBeforeShow, onBeforeHide, onInit, and onUninit by passing an option object to the constructor of SettingsPanel.

Implementation Guide

How to create a new panel in Settings?

1. Create an HTML template

Create the template with the following format and place it under elements/.

<element name="{panel_name}" extends="section">
    <!-- UI elements -->

2. Import the HTML template to index.html

Add the following link tag to the head element of index.html.

<link rel="import" href="{path_to_html_template}">

3. Create the placeholder for populating the HTML template

Add the following section tag in the body element of index.html. Typically panel_id and panel_name is identical.

<section is="{panel_name}" role="region" id="{panel_id}"></section>

How to load scripts for a panel?

1. Define an AMD module for the panel

All dependent scripts should be loaded following the AMD pattern. Usually a panel module is extended from SettingsPanel to have the ability of automatic binding to the settings database. You can choose to extend from Panel if you would like to handing the binding by yourself or the panel does not need the database at all. Require other depedent modules in the modeul definition. A simple module looks like:

define(function(require) {
  var SettingsPanel = require('modules/SettingsPanel');
  var Module1 = require('modules/Module1');
  var Module2 = require('modules/Module2');

  return SettingsPanel({
    onInit: function(rootElement, initOptions) {
      // ...
    onUninit: function() {
      // ...
    onShow: function(rootElement, showOptions) {
      // ...
    onHide: function() {
      // ...

2. Add the module to the HTML template

A panel module could be loaded by adding a tag with a data-path attrbute specifying the panel module in the end of the template. The template will look like:

<element name="{panel_name}" extends="section">
    <!-- UI elements -->
    <panel data-path="{path_to_panel_module}"></panel>

Note that there should be only one panel module specified in the template. All other dependent modules should be required in the panel module. SettingsPanel is used by default if no panel module is specified.

All panels should be defined in the folder under panels/ with the name identical to the panel's name. ex: battery panel should be defined in panels/battery folder.

How to port an existing panel to follow the new architecture design?

Basically this could be done by following the previous two sections. Create a panel module and require the dependent modules converted from the original scripts, then add the panel module to the HTML template. Details are explained in the following.

1. Create a new panel module

Follow this section to create a new panel module and add it to the corresponding HTML template that could be found under elements/. The panel module must be placed under panels/<panel_name>/ and named as panel.js. Remember to remove all script tags in the template because they should be required in the panel module.

2. Convert original scripts to AMD modules

Examine all dependent scripts carefully and convert them to reusable modules. Reusable means that the modules should not be bound to fixed UI elements so that we have the flexibility doing the binding dynamically. It also implies that the unit tests no longer depend on UI elements, which makes writing tests more easily.

3. Load the modules in the panel module

The panel module created in the first step is the start point of each panel and it should be responsible for loading all dependent modules. Note that we should use sugared syntax when loading the modules and avoid naming the module explicitly.

4. Configure module settings

Settings app utilizes r.js in the build process. It produces module scripts based on the configuration file, settings/js/config/require.js. The following object in the modules array in the configuration file specifies a module:

  name: '{path_to_panel_module}',
  exclude: ['main']

All dependent modules of the specified module except for the modules listed in the exclude array will be merged into one file in the build process. This allows that all code required code could be loaded at once when a panel is navigated.

5. Run integration tests

Run the tests with the following command to ensure the refactoring does not break the anything.

$ make test-integration APP=settings

Build Steps

Settings app has it's own Makefile. A Makefile is similar to Grunt, but written in bash. It is essentially a list of tasks that can be run (via make <task-name>). When a Gaia application has its own apps/<app-name>/Makefile, it will be automatically run when Gaia builds.

Our Makefile has two tasks, one to 'build' and one to 'clean' (delete the build). The build steps are as follows:

  1. Remove any previous settings build from the build_stage/
  2. Create an new directory build_stage/settings
  3. Run the r.js (RequireJS optimizer), pointing it at our require_config.jslike file (.jslike because we don't want Gaia builds to mess with it [I think]). This copies our entire application (JS and all) and bundles our JS (tracing require() calls) and CSS (tracing @import) in two single files.


How to make sure some specific works are done before rendering panels ?

Sometimes, you may need to do something before rendering panels. In order to achieve this, you have to return a promise object in onBeforeShow first and Settings app will do the transition after the promise is resolved. By the way, don't put some really heavy works here, otherwise users will feel confused and would treat Settings app as broken.

return SettingsPanel({
  onBeforeShow: function _onBeforeShow() {
    var promise = new Promise(function(resolve, reject) {
      // do your works here
      // then call the resolve method from Promise instance
      fetch_data_from_server(function callback() {

    // Return the promise object back to Settings app
    return promise;