View source for Gaia/System/NewModule

If you want to add a new functionality, a.k.a., a new script or a new module into system app after bug 1094759,
please read this.

== If you want to use BaseModule ==
Great! It's providing a promise based start procedure and what you need to do.

  var NewModule = function() {};
  BaseModule.create(NewModule, {
    name: 'NewModule',
    _start: function() {
      // return a promise if your start progress involves some asynchronous operation
      // return null or do not return, then we will unblock your module from the starting process right away once
      // yourModule.start() is called
      // BaseModule has a native start() function to process not only your own starting (this._start()) but also the child
      // module's start() function. The whole starting process will be resolved only when all the children's start process
      // is resolved.
    }
  });

== If you don't want to use BaseModule ==
It's okay. But you have to provide this interface for us:

  var NewModule = {
    start: function() {
      // return a promise if your start progress involves some asynchronous operation
      // return null or do not return, then we will unblock your module from the starting process right away once
      // yourModule.start() is called
    }
  };

== No matter what you choose to go ==
Don't put your new script in the header of system app.
If it's necessary to go alive when booting, please find a proper parent module and lazy load it.

=== If the parent module is based on BaseModule ===
# Put the module in the parent module's SUB_MODULES if you think it's blocking the starting progress of the parent module.
# If the new module is not as important to block the parent, use this.loadWhenIdle([NEW_MODULE]) in parent's start function
# If the new module is only serving some on demand request, consider to lazy load the new module in the parent module's event handler and start it.

=== If the parent module is not based on BaseModule ===
# Lazy load the module in the parent module's start function and return a promise including the promise of the lazy loader
# If the new module is only serving some on demand request, consider to lazy load the new module in the parent module's event handler and start it.

== Samples ==
In the following sample,
1. Core is an existing module who blocks the first view
2. ParentModule is an existing module who does not block the first view
=== Sample for the module which does block the first view and the parent module is a base module ===
  // ftu_loader.js
  var FtuLoader = function() {};
  BaseModule.create(FtuLoader, {
    name: 'FtuLoader',
    _start: function() {
      return LazyLoader.load('shared/js/test.js').then(() => {
        // Do something...
      });
    }
  });

  // core.js
  Core.SUB_MODULES = ['FtuLoader'];

=== Sample for the child module which does not block the first view and the parent module is a base module ===
  // side_tester.js
  var SideTester = function() {};
  BaseModule.create(SideTester, {
    name: 'SideTester',
    _start: function() {
      return LazyLoader.load('shared/js/async.js').then(() => {
        // Do something...
      });
    }
  });

  // core.js
  BaseModule.create(Core, {
    _start = function() {
      return this.loadWhenIdle(['SideTester']);
    };
  });

=== Sample for the new module which does not block the first view and the parent is not a baseModule ===
  // side_tester.js
  var ChildModule = function() {};
  ChildModule.prototype.start = function() {};

  // parent_module.js
  ParentModule.prototype.start = function() {
    return Service.request('schedule', () => {  // This is exactly what BaseModule.prototype.loadWhenIdle does
      return LazyLoader.load('child_module.js');
    }).then(() => {
      this.child = new ChildModule();
      return this.child.start();
    });
  };