Universal Framework

Previous sections have mentioned that Fusion.js runs through all code both on the server and on the client. This differs from traditional frameworks where there is a clear delineation between what code is for the server and what code is for the client.

For code that is just rendering components, that is ok. However, for libraries that deal with file system access or accessing browser API's, there needs to be a way to specify which code is environment specific and not universal. Fusion.js provides global constants for this purpose that are defined during build time. Let's take a look at an example:

const app = new App();

// This plugin is universal and works across both environments

// These plugins ONLY work on the server
if (__NODE__) {

// These plugins ONLY work on the browser
if (__BROWSER__) {

The above entrypoint file uses the __NODE__ and __BROWSER__ constants to delineate which logic runs in which environments. We call these code fences. When Fusion.js code is built, the compiler will remove all code from a bundle if it does not match the given environment. So the server bundle will not have code marked as __BROWSER__ only and vice versa.

These constants can be used across all universal code and help to contain code that belongs in the same environment together. Along with Webpack tree shaking configured out of the box, this process keeps your Javascript bundles optimized and lean for maximum performance.


One common theme with universal code is the need to scaffold the code on the server, serialize the current state onto the client, and then hydrate that state when the client loads. For example, serializing the current Redux store into a <script> tag and then reading from that tag to populate the client side store with the same state.

For example, here is the Redux code on the server for Express that renders and then writes the current state onto the page:

function handleRender(req, res) {
  // Create a new Redux store instance
  const store = createStore(rootReducer)

  // Render the component to a string
  const html = renderToString(
    <Provider store={store}>
      <App />

  // Grab the initial state from our Redux store
  const preloadedState = store.getState();

  // Send the rendered page back to the client
      <div id='root'>${html}</div>
      <script id='redux-state'>JSON.stringify(preloadedState)</script>

And here is the associated client code:

const preloadedState = JSON.parse(document.getElementById('redux-state'));

const store = createStore(rootReducer, preloadedState);

const app = (
  <Provider store={store}>
    <App />

render(app, document.getElementById('root'));

This pattern applies for other libraries as well and causes this initialization code to be spaghettied across your code base.

In Fusion.js, this logic can be encapsulated into a single plugin, resulting in far cleaner code and a clear abstraction between application code and plugin code:

const app = new App(root);
// ReduxPlugin handles creating the <Provider> and store and wrapping your root element inside of it
app.register(ReduxToken, ReduxPlugin);
// ReducerToken allows for registering a root reducer into the plugin
app.register(ReducerToken, reducer);

One code base

Working in Fusion.js can be different than other frameworks because the code that you are writing is one shared code base. We believe that working with only one code base simplifies overhead in figuring out how to structure your project to ensure which code is run where, how to set up your compiler configs to write out the right bundles, and making sure your web app is architected correctly. Using code fences helps to separate out your environmental specific logic when you it.

In the next section, we'll cover the different packages that make up the framework.