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

import React from 'react'
import { Provider } from 'mobx-react'
import { getSnapshot } from 'mobx-state-tree'
import App, { Container } from 'next/app'
import { initializeStore } from '../stores/store'

export default class MyApp extends App {
  static async getInitialProps ({ Component, router, ctx }) {
    //
    // Use getInitialProps as a step in the lifecycle when
    // we can initialize our store
    //
    const isServer = (typeof window === 'undefined')
    const store = initializeStore(isServer)
    //
    // Check whether the page being rendered by the App has a
    // static getInitialProps method and if so call it
    //
    let pageProps = {}
    if (Component.getInitialProps) {
      pageProps = await Component.getInitialProps(ctx)
    }
    return {
      initialState: getSnapshot(store),
      isServer,
      pageProps
    }
  }

  constructor (props) {
    super(props)
    this.store = initializeStore(props.isServer, props.initialState)
  }

  render () {
    const { Component, pageProps } = this.props
    return (
      <Container>
        <Provider store={this.store}>
          <Component {...pageProps} />
        </Provider>
      </Container>
    )
  }
}