next.js/lib/app.js

import React, { Component, PropTypes } from 'react'
import { AppContainer } from 'react-hot-loader'
import shallowEquals from './shallow-equals'

const ErrorDebug = process.env.NODE_ENV === 'production'
  ? null : require('./error-debug').default

export default class App extends Component {
  static childContextTypes = {
    headManager: PropTypes.object
  }

  getChildContext () {
    const { headManager } = this.props
    return { headManager }
  }

  render () {
    const { Component, props, hash, err, router } = this.props
    const url = createUrl(router)
    const containerProps = { Component, props, hash, router, url }

    return <div>
      <Container {...containerProps} />
      {ErrorDebug && err ? <ErrorDebug error={err} /> : null}
    </div>
  }
}

class Container extends Component {
  componentDidMount () {
    this.scrollToHash()
  }

  componentDidUpdate () {
    this.scrollToHash()
  }

  scrollToHash () {
    const { hash } = this.props
    const el = document.getElementById(hash)
    if (el) {
      // If we call scrollIntoView() in here without a setTimeout
      // it won't scroll properly.
      setTimeout(() => el.scrollIntoView(), 0)
    }
  }

  shouldComponentUpdate (nextProps) {
    // need this check not to rerender component which has already thrown an error
    return !shallowEquals(this.props, nextProps)
  }

  render () {
    const { Component, props, url } = this.props

    // includes AppContainer which bypasses shouldComponentUpdate method
    // https://github.com/gaearon/react-hot-loader/issues/442
    return <AppContainer errorReporter={ErrorDebug}>
      <Component {...props} url={url} />
    </AppContainer>
  }
}

function createUrl (router) {
  return {
    query: router.query,
    pathname: router.pathname
  }
}