How to modularize AngularJS applications / plugins

Question

I have a couple of (software-)architecture questions regarding a migration from Grails (REST-API, parts of AngularJS, MongoDB, Tomcat, Spock, several plugins) to Node.js + Angular.js. I probably have to explain the structure of the Grails project fist, so here we go:

There is a main Grails application (beside a couple of other applications), which is built on several plugins. Each of these plugins is able to get executed by itself - that means it has its own UI, individual templates, services, controllers, routes, tests etc. It is also hosted on different repositories. This is done by the Grails plugin mechanisms. The benefits are less testing-efforts, less compiling time, modularization, single responsibilities and so on.

But still, the time to compile and test are too expensive. Also I don't like the fact that the API delivers parts of the templates/views. I would like to have the backend APIs "just to be backend APIs" and the frontend "just to be the frontend". So each AngularJS application/plugin will provide its own view, routes, service etc. But they might also depend on other plugins.

So what I would like to achieve is as follow:

• One main AngularJS application, which includes several plugins (a plugin can be something like a report-generator, a guestbook or whatsoever, speaking of a single independent part of an application, either with a specific route, or just a small part of the page).
• Each plugin must be a stand-alone AngularJS application (probably executable during development via grunt or so). So that the UI developer does not need to start the whole backend application, further that we may run functional tests only with JavaScript
• Communication only via REST, The frontend must retrieve all it's data from the APIs
• Each plugin must be testable on its own
• A Plugin might require other plugins to work
• The main index.html (and app.js?) might be provided by a Nginx server, which is decoupled from the rest of the backend (API)

Though I have a specific picture in my head, I am struggling in how to setup this architecture.

In Grails the plugin mechanisms are somehow merging the plugin dependant settings (like URL mappings, dependencies, etc) to the main application in which they get included/injected - this is what I want to achieve with AngularJS as well. So:

• Are there some kind of same mechanisms for AngularJS?
• How may I provide/merge the routes of each plugin into the main application?
• How can I declare application- and plugin-dependencies?
• What tools might be usefull for the build process?
• How to establish lazy-retrievments of the plugin-resources (css/less files, views, services etc)?
• Prevent the application to provide all resources of the plugins on startup (I guess the routes are required on startup though)

Since this is not just a how-to-do-this-or-that question I excuse myself if I am missing important parts or if some parts are not clear enough. Just ask me and I will answer each question in depths.

Answer 1

** This answer is incomplete **

I want to make sure I understand you before I dig into this.

Here's a quick implementation of a Loader module to manage lazy loading (plugins, vendor assets, admin stuff etc).

Does this help?

angular.module('Bizcoin.loader')
.service('Loader', Loader);

function Loader($injector, $ocLazyLoad, User) {
  var Loader = {
    load: load,
    get: get,
    plugins: {},
    flags: {}
  };

  init();

  return Loader;

  function init() {
    load('vendors');
    if (userIsAdmin)
      load('admin');
  }

  function load(plugin) {
    Loader.plugins[plugin] = Loader[plugin] || $ocLazyLoad.load('path/to/'+plugin+'.js');
    return Loader.plugins[plugin].then(setFlag);

    function setFlag() {
      return Loader.flags[plugin] = true;
    }
  }

  function get(plugin) {
    return load(plugin).then(function() {
      return $injector.get(plugin);
    });
  }

}

Answer 2

I work on an large .Net/AngularJS application that is composed of 20+, independent, Areas (or modules) and some core functionality common and reused across all Areas.

Let me go into detail on how I do this for my particular case, and it might give some ideas. The fact that I use .Net is irrelevant here, since this can achieve with any framework.

Each Area acts as an independent application that depends only on the core functionality, always present. Each Area has its own ASP.Net MVC route. Each Area registers with the core application the menu links it wants to provide. When the customer goes to the application dashboard, only the core part of of the application. When the user clicks on link in the menu, it will navigate to the content provided by one of the Areas, and only the core plus the assets of that Area are loaded.

Lets see how this is done.

In the main page of the application I load the scripts like this:

<script type="text/javascript">
    // a JS object with all the necessary app data from the server.
    // e.g.: menu data, etc
    window.appContext = @Html.Action("ApplicationContext", "Portal")); 
</script>

@Scripts.Render("~/bundles/angular-main")

@RenderSection("AngularAreas", required: false)

I make use of dot .Net bundles and sections.

The main (core) AngularJS part of the application consists of angular configuration, internationalization services, global notifications service, reusable UI components, etc. This is loaded is @Scripts.Render("~/bundles/angular-main").

The @RenderSection("AngularAreas", required: false) section will be filled in by each area when the user navigates to that Area.

Lets see some AngularJS code. Here is part of the main app.ts.

// If user is visiting an Area, the NgModules array will be augmented.
// with the modules the Area wants to provide (to be bootstrapped)
export var LoadNgModules = [
    NgModules.Config,
    NgModules.Core
];

angular.module(NgModules.Bootstraper, LoadNgModules);

angular.element(document).ready(function () {
    angular.bootstrap(document, [NgModules.Bootstraper]);
});

Lets look at an example Area now.

And here is how an Area would supply its assets, to be outputted in @RenderSection("AngularAreas", required: false):

@section AngularAreas {
    @Scripts.Render("~/bundles/areas/staff-management")
}

Its a simple bundle containing all the scripts for that Area. Now, let's see the important part of the AngularJS code for this Area.

var StaffManagementNgModule = 'areas.staff-management';

// Push our self into the modules to be bootstrapped
LoadNgModules.push(StaffManagementNgModule );

// Define the module
angular
    .module(StaffManagementNgModule , ['ngRoute', NgModules.Core])
    .config([
        '$routeProvider', '$locationProvider', ($routeProvider: ng.route.IRouteProvider, $locationProvider) => {

            $routeProvider
                .when(staff', { template: '<staff></staff>' })
                .when('staff/details/:id', { template: '<staff-details></staff-details>' });
        }
    ]);;

That is all, from here the Area is a normal Angular application.

To summarize, we load the main (core) AngularJS functionality and provide the LoadNgModules array that an area can fill with its own modules.

we load the Area scripts and and "our self" to the LoadNgModules array.

finally the run angular.bootstrap.

For completeness, here is a fragment of C# showing how an area would indicate to the main application that it is available

public class ItemManagementModuleRegistration : IModuleRegistration
{
    public void Register(ModuleContext moduleContext)
    {
        string thisAreaName = "Staff";

        moduleContext.RegisterMenu(menuContext =>
        {
            var ItemsMenu = menuContext.Items(thisAreaName);

            // add urls and stuff...
        });

        // register more stuff with the moduleContext
    }
}

Using reflection one can easily find what areas are "installed".

These are the main moving parts of the setup. Each Area can have its own API and tests. It is quite flexible.