next.js/examples/with-next-page-transitions/pages/_app.js

import React from 'react'
import App, { Container } from 'next/app'
import { PageTransition } from 'next-page-transitions'

import Loader from '../components/Loader'

const TIMEOUT = 400

export default class MyApp extends App {
  static async getInitialProps ({ Component, ctx }) {
    let pageProps = {}

    if (Component.getInitialProps) {
      pageProps = await Component.getInitialProps(ctx)
    }

    return { pageProps }
  }

  render () {
    const { Component, pageProps } = this.props
    return (
      <Container>
        <PageTransition
          timeout={TIMEOUT}
          classNames='page-transition'
          loadingComponent={<Loader />}
          loadingDelay={500}
          loadingTimeout={{
            enter: TIMEOUT,
            exit: 0
          }}
          loadingClassNames='loading-indicator'
        >
          <Component {...pageProps} />
        </PageTransition>
        <style jsx global>{`
          .page-transition-enter {
            opacity: 0;
            transform: translate3d(0, 20px, 0);
          }
          .page-transition-enter-active {
            opacity: 1;
            transform: translate3d(0, 0, 0);
            transition: opacity ${TIMEOUT}ms, transform ${TIMEOUT}ms;
          }
          .page-transition-exit {
            opacity: 1;
          }
          .page-transition-exit-active {
            opacity: 0;
            transition: opacity ${TIMEOUT}ms;
          }
          .loading-indicator-appear,
          .loading-indicator-enter {
            opacity: 0;
          }
          .loading-indicator-appear-active,
          .loading-indicator-enter-active {
            opacity: 1;
            transition: opacity ${TIMEOUT}ms;
          }
        `}</style>
      </Container>
    )
  }
}