vercel__next.js/examples/with-userbase/pages/_app.js

import { useState, useEffect } from "react";
import userbase from "userbase-js";
import Layout from "../components/layout";

import "../styles/index.css";

function MyApp({ Component, pageProps }) {
  const [user, setUser] = useState();

  useEffect(() => {
    userbase.init({ appId: process.env.NEXT_PUBLIC_USERBASE_APP_ID });
  }, []);

  return (
    <Layout user={user} setUser={setUser}>
      <Component user={user} {...pageProps} />
    </Layout>
  );
}

export default MyApp;