meta-spa-router: A lightweight and solid approach towards micro frontends (SPAs/ clients for micro services)

Features

• Meta Router for creating a shell app that loads micro frontends (aka routed applications or child apps) using iframes
• Because of the usage of iframes the micro frontends are isolated and cannot influence each other in an unplanned way.
• Allows using different frameworks in different versions for the loaded micro frontends.
• iframes are created at runtime
• Allows jumping to a specific route within a child app
• Synchronizing child app's routes with the shell's route
• Resizes the iframes to prevent a scrollbar within the iframe
• Tested with Hash-based routing
• Tested w/ Chrome, Firefox, Edge and IE 11 (IE needs polyfills)
• Allows Angular-like Aux-Routes to show several micro frontends side by side at one time

Installation

npm install meta-spa-router --save

Usage

Setting up the routes in the shell app:

var MetaRouter = require('meta-spa-router').MetaRouter;

var config = [
    {
        path: 'a',
        app: '/app-a/dist'
    },
    {
        path: 'b',
        app: '/app-b/dist'
    }
];

window.addEventListener('load', function() { 

    var router = new MetaRouter();
    router.config(config);
    router.init();
    router.preload();


    document.getElementById('link-a')
            .addEventListener('click', function() { router.go('a') });

    document.getElementById('link-b')
            .addEventListener('click', function() { router.go('b') });

    document.getElementById('link-aa')
            .addEventListener('click', function() { router.go('a', 'a') });

            document.getElementById('link-ab')
            .addEventListener('click', function() { router.go('a', 'b') });        

}); 

Setting up the routed client apps (Framework agnostic way):

    import { RoutedApp } from 'meta-spa-router';

    let routedApp = new RoutedApp();

    routedApp.config({ appId: 'a' });
    routedApp.init();

    [...]

    // When we change the route in the client app, tell the shell about it:
    routedApp.sendRoute(e.url);

    // When the shell changes the route, we have to tell our router about it:
    routedApp.registerForRouteChange(url => /* delegate url to your app's router */);

Please note that by convention the appId is the same as its path in the shell app.

The example below uses Angular and it's DI system for this task.

Example

• see folder sample in the libs repo.
• see index.js for setting up the meta routes
• see app-a/src/app/app.module.ts - Even though this works with any framework, this client app uses Angular and it's Dependency Injection (DI) system. In this file, the ChildApp class is registered as a service. Instead of this you could also instanciate it directly when going with an other framework.
• see app-a/src/app/app.component.ts for initializing child apps. Again, using Angular's DI which is not a condition.

Trying it out

1. Install the libs for each child app and build them:

    cd app-a
    npm install
    npm run build

    cd ..

    cd app-b
    npm install
    npm run build

    cd ..

2. Do the same for the shell app:

    npm install
    npm run build

2. Start the shell app with a web server of your choice, e. g. http-server

    npm install -g http-server
    http-server -o

Aux Routes

You can use Angular-like Aux Routes that allows to load several micro frontends at the same time. To use this feature just define several outlets. You can use any id while the value outlet is used for the default route:

<div id="outlet"></div>
<div id="outlet2"></div>

After this, you can define per route for which outlet it is indented. If you skip the outlet property, the outlet with the id outlet is used:

var config = [
    {
        path: 'a',
        app: '/app-a/dist'
    },
    {
        path: 'b',
        app: '/app-b/dist',
        outlet: 'outlet2'
    }
];

To load a micro frontend into those outlets, just use the go method:

    router.go('a'); // loads a into (default) outlet
    router.go('b'); // loads b into outlet2 (see above)

Trying out Aux Routes

Please find an example for Aux Routes in the folder sample-aux. To install the dependencies and run it, you can use the commands described for the other sample above.

Blog

More infos about this and Angular can be found on my blog.