# MobX 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.

![](http://i.imgur.com/JCxtWSj.gif)

This example is a mobx-react-lite port of the [with-mobx](https://github.com/vercel/next.js/tree/master/examples/with-mobx) example. MobX support has been implemented using React Hooks.

## Deploy your own

Deploy the example using [Vercel](https://vercel.com):

[![Deploy with Vercel](https://vercel.com/button)](https://vercel.com/import/project?template=https://github.com/vercel/next.js/tree/canary/examples/with-mobx-react-lite)

## How to use

### Using `create-next-app`

Execute [`create-next-app`](https://github.com/vercel/next.js/tree/canary/packages/create-next-app) with [npm](https://docs.npmjs.com/cli/init) or [Yarn](https://yarnpkg.com/lang/en/docs/cli/create/) to bootstrap the example:

```bash
npx create-next-app --example with-mobx-react-lite with-mobx-react-lite-app
# or
yarn create next-app --example with-mobx-react-lite with-mobx-react-lite-app
```

### Download manually

Download the example:

```bash
curl https://codeload.github.com/vercel/next.js/tar.gz/canary | tar -xz --strip=2 next.js-canary/examples/with-mobx-react-lite
cd with-mobx-react-lite
```

Install it and run:

```bash
npm install
npm run dev
# or
yarn
yarn dev
```

Deploy it to the cloud with [Vercel](https://vercel.com/import?filter=next.js&utm_source=github&utm_medium=readme&utm_campaign=next-example) ([Documentation](https://nextjs.org/docs/deployment)).

## Implementation details

The initial store data is returned from the `initializeData` function that recycles existing store data if it already exists.

```jsx
function initializeData(initialData = store || {}) {
  const { lastUpdate = Date.now(), light } = initialData
  return {
    lastUpdate,
    light: Boolean(light),
  }
}
```

The observable store is created in a function component by passing a plain JavaScript object to the `useObservable` hook. Actions on the observable store (`start` and `stop`) are created in the same scope as the `store` in `store.js` and exported as named exports.

```js
store = useObservable(initializeData(props.initialData))

start = useCallback(
  action(() => {
    // Async operation that mutates the store
  })
)

stop = () => {
  // Does not mutate the store
}
```

The component creates and exports a new React context provider that will make the store accessible to all of its descendents.

```jsx
return <StoreContext.Provider value={store}>{children}</StoreContext.Provider>
```

The store is accessible at any depth by using the `StoreContext`.

```js
const store = useContext(StoreContext)
```

The clock, under `components/Clock.js`, reacts to changes in the observable `store` by means of the `useObserver` hook.

```jsx
return (
  <div>
    // ...
    {useObserver(() => (
      <Clock lastUpdate={store.lastUpdate} light={store.light} />
    ))}
    // ...
  </div>
)
```