next.js/examples/with-mobx-state-tree

MobX State Tree example

How to use

Download the example or clone the repo:

curl https://codeload.github.com/zeit/next.js/tar.gz/canary | tar -xz --strip=2 next.js-canary/examples/with-mobx
cd with-mobx

Install it and run:

npm install
npm run dev

Deploy it to the cloud with now (download)

now

Notes

This example is a mobx port of the with-redux example. Decorator support is activated by adding a .babelrc file at the root of the project:

{
  "presets": [
    "next/babel"
  ],
  "plugins": [
    "transform-decorators-legacy"
  ]
}

Rehydrating with server data

After initializing the store (and possibly making changes such as fetching data), getInitialProps must stringify the store in order to pass it as props to the client. mobx-state-tree comes out of the box with a handy method for doing this called getSnapshot. The snapshot is sent to the client as props.initialState where the pages's constructor() may use it to rehydrate the client store.

The idea behind the example

Usually splitting your app state into pages feels natural but sometimes you'll want to have global state for your app. This is an example on how you can use mobx that also works with our universal rendering approach. This is just a way you can do it but it's not the only one.

In this example we are going to display a digital clock that updates every second. The first render is happening in the server and then the browser will take over. To illustrate this, the server rendered clock will have a different background color than the client one.

Our page is located at pages/index.js so it will map the route /. To get the initial data for rendering we are implementing the static method getInitialProps, initializing the mobx-state-tree store and returning the initial timestamp to be rendered. The root component for the render method is the mobx-react <Provider> that allows us to send the store down to children components so they can access to the state when required.

To pass the initial timestamp from the server to the client we pass it as a prop called lastUpdate so then it's available when the client takes over.

The trick here for supporting universal mobx is to separate the cases for the client and the server. When we are on the server we want to create a new store every time, otherwise different users data will be mixed up. If we are in the client we want to use always the same store. That's what we accomplish on store.js

The clock, under components/Clock.js, has access to the state using the inject and observer functions from mobx-react. In this case Clock is a direct child from the page but it could be deep down the render tree.

As far as how this example differs from the with-mobx example, mobx-state-tree requires that any changes to the observable data are sent as actions, which are defined on the model in server.js. The snapshot feature, while not very useful in this particular case, makes client-side rehydration of the state amazingly easy. Any changes that are made to the store in getInitialProps will be refreshed instantly when that page is loaded on the client.