Effortlessly host your React app on both the client and the server. Some call it isomorphic JavaScript - we call it Ambidex.


58670.2.0-beta.126 years ago7 years agoMinified + gzip package size for ambidex in KB




Ambidex lets you render the exact same React.js app on both the client and the server. It abstracts away the differences between them, so you can focus your creativity where it matters most: on your product.

eBay Open Source
Ambidex is being incubated in the eBay Mobile Innovations lab.



Ambidex brings together the best of a bunch other fantastic projects, including:


Ambidex has been tested on

  • iojs v1.0.1
  • npm v2.2.0

It should also work on node v0.11.13 with the --harmony flag, but no promises.


Ambidex is a work-in-progress. It is the foundation of our web-centric work in the eBay Mobile Innovation lab, but it has not yet been deployed in production.

It is being developed in the open so we, as a community, can share ideas and best practices around being insanely productive with React. When you see something you'd like to improve, please start an issue or send us a message.

How it works

Ambidex renders the initial request on the server and subsequent requests in the browser. Rendering on the server is beneficial for SEO, time-to-glass, and supporting clients that don't speak JavaScript (like robots). Rendering on the client saves bandwidth, reduces server load, and makes your app feel more responsive (because changes happen instantly). Ambidex brings you the benefits of both.

It is designed to be used in conjunction with a Service-Oriented Architecture. This means your data layer should be provided as a RESTful API that functions independently of your web app.

This architecture has two advantages:

  1. Your data platform is capable of supporting any client, including native mobile apps or those of third parties.

  2. Your app can access data directly from the browser, so it doesn't waste server cycles requesting largely-redundant HTML on every page load.

Getting Started

(Dive right in by perusing our sample application.)

Here's how you instantiate Ambidex:

new Ambidex(
    "settings":             require(`./settings.${ process.env["NODE_ENV"] }.js`),

    "middlewareInjector":   function (stack) {
                              // If you want to edit your Mach stack (for instance, 
                              // to serve static files with mach.file) do that here.
  (ambidex) => {


Notice that the Ambidex constructor returns a promise. This promise will be resolved when your app is serving as expected.

Each Ambidex instance has three public properties:

  • ambidex.stack: the Mach stack that is serving your app,
  • ambidex.webpack: the Webpack instance that bundles your files, and
  • ambidex.webpackDevServer: the Webpack Dev Server instance that serves your files when ENABLE_HOT_MODULE_REPLACEMENT is true.


Each instance of Ambidex starts with a settings dictionary. Here are the individual settings supported:


The name your app will be referred to in the logs, "My Awesome App".

settings["SHORT_NAME"] (optional)

A variation of that name without spaces or capital letters - your app will appear in process monitors like top under this name, "my_awesome_app"


The hostname that your app will be made available at, "".


The port that goes in your browser's address bar, "80".

settings["VM_PORT"] (optional)

If your app is behind a load balancer, this is the port that Ambidex should serve your app so the load balancer can find it, "8080".

settings["BASE_URL"] (optional)

If your app is behind displayed inside a TardisGallery, mount its route tree here. This allows you to serve different variations of your app alongside one another; for instance, you might serve version A at "/A/" and version B at /B/.

settings["ENABLE_HOT_MODULE_REPLACEMENT"] (optional)

If this is true, you'll be able to edit your app live with react-hot-loader. This should be true for whatever environment(s) you're developing on.

settings["TITLE_SEPARATOR"] (optional)

This string gets put in between section titles, such as " - ".


For instance, "/static/logo.svg".


In order to make your app Ambidextrous, we need to know where certain files are kept. The values in this dictionary answer that question.


All the other FILESYSTEM_PATHS are relative to this one. If you set this to __dirname (no quotes), they will be relative to your settings file.


The module at this path should export the root <Route> of your route tree.

settings.FILESYSTEM_PATHS["STYLES"] (optional)

By default, Ambidex will set the same defaults as React Native, such as using flexbox for all block-level elements. It also defaults to Roboto, the Material Design font used across Android.

If you'd like to override those defaults, simply point FILESYSTEM_PATHS["STYLES"] your own CSS file.


This module should export a dictionary of Funx definitions, e.g.:

module.exports = {
  "apiDefinitions":     {
                          "Bikes":        require("./apis/Bikes.js"),

  "storeDefinitions":   {
                          "stateful":   {
                                          "Bikes":        require("./stores/Bikes.js"),
                          "ephemeral":  {
                                          "currentBike":    function (Bikes, routerState) {
                                                              return routerState.has("bikeID")
                                                                ? Bikes.getOrFetch(
                                                                      "bikeID":  routerState.get("bikeID")
                                                                : null

                                          "readyToRender":  function (routerState, currentBike) {
                                                              if (routerState.has("bikeID") && !currentBike)
                                                                return false;

                                                              return true;

Until I have time to document this better, see Gravel's funxDefinitions for a very simple example.


When "ENABLE_HOT_MODULE_REPLACEMENT" is false (e.g. in production), Ambidex will run Webpack on all your files and serve the results inline in every response. To do so, it need to be able to cache them on the filesystem.

"BUNDLES" should resolve to a folder where it can store these files. Each instance of Ambidex needs its own unique bundles folder.

settings["SERVER_ONLY_MODULE_NAMES"] (optional)

This is an array of module names that should be ignored by Webpack because they are not compatible with the browser (and will only ever run on the server). For instance, ["jsdom"].

settings["CUSTOM_SETTINGS"] (optional)

settings is just a dictionary - you can put any values inside it that you find useful. For instance, you might add "STATIC_URL" so your components know which CDN hosts your static assets.

However, as Ambidex evolves, so too will the available settings. To ensure new features don't collide with your app-specific inclusions, put any settings that Ambidex won't consume in settings.CUSTOM_SETTINGS.

Remember, because your routes need to be compiled to JavaScript source code to be run on the client, anything you put in here needs to survive JSON serialization.

Organizing your settings files

Of course, you'll need different settings for your production server than you will for your local machine, but nobody wants to maintain the same information in many places. Therefore, it's a common pattern to have a separate settings file for each environment you'll need, and one more that holds everything that they all share.

For instance, a professional project that utilizes many environments might be organized like this:

Each of those will include and extend (or even override) settings.common.js. They should be very small files that describe only what is unique about that environment.


There are subtle differences between the ways the client and server operate. We need to abstract them out to make your app Ambidextrous. That's what these mix-ins are for.


Any route handler can include the Title mix-in.

When your route tree renders, Ambidex will check each handler for a section title:

settings["TITLE_SEPARATOR"] will be interspersed between each section title. The result will be returned in the <title> tag when rendered on the server, or set on the client with document.title.


The biggest difference between running your app on the server and running it on the client is how you load data when someone clicks a link:

  • The server only gets to respond once, so it must wait until every piece of data has loaded before responding.

  • The client doesn't have this limitation, and users expect it to respond immediately. The best strategy here is to change pages immediately (even though your stores are probably empty) and to fill the component with new data as it arrives.

The first challenge to overcome is knowing which data needs to be loaded for a particular page to be rendered. The server only knows which page to show by inspecting the URL; it can also use the URL determine which data to load.

You can create named parameters in ReactRouter by placing a colon before the parameter name. For example, this route has a single named parameter, bikeID:

  path    = "/bikes/:bikeID/edit/"
  name    = "editBike"
  handler = { require('./bike-index/components/BikeDetails.jsx') }

When Ambidex renders a route, it receives a state object from ReactRouter. It puts all of state's parameters into an Immutable Map and wraps it in a Funx store called routerState. Listen for routerState from your ephemeral stores to expose particular subsets your stateful stores.

You must provide an ephemeral store called readyToRender that listens returns true when all your data dependencies are loaded and ready to be handed to the client.

See an example of using routerState and creating a readyToRender store in the funxDefinitions section.

Now that you've sorted out what data needs to be loaded, you need to pass it to your React components.

The best way is with Ambidex.mixinCreators.connectStoresToLocalState(storeNames). It will listen to the specified stores and persist their most recent values on your component's state. Whenever a store updates, your component will too.

If you'd rather do it manually, you can instead use Ambidex.mixins.Funx, which adds getFunxAction and getFunxStore methods to your components.


It can be really useful to access the combined settings dictionary from your components. Simply mix in Settings and call this.getAmbidexSettings() from inside your component.

If you find any bugs or have a feature request, please open an issue on github!

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