Start Next.js if behind passenger

app.ts

// I found bad advice online on how to use Next.js behind passenger https://www.phusionpassenger.com/
// yarn start or npm start won't work. This file is derived from the code that runs when you
// run the yarn start command. Tested only in my particular setup where the file is required
// to be called app.js. This file is TS, so you'll need to transpile to JS in your build, 
// eg change package json build script to (you'll need a tsconfig.server.json file):
// "build": "next build && tsc --project ./tsconfig.server.json",

import http from 'http';
import next from 'next';

async function start(opts: any, port?: number, hostname?: string) {
    const app = next({ ...opts, customServer: false });
    const srv = http.createServer(app.getRequestHandler());

    await new Promise<void>((resolve, reject) => {
        // This code catches EADDRINUSE error if the port is already in use
        srv.on('error', reject);
        srv.on('listening', () => resolve());
        srv.listen(port, hostname);
    });
    // It's up to caller to run `app.prepare()`, so it can notify that the server
    // is listening before starting any intensive operations.
    return app;
}

const port = parseInt(process.env.NODE_PORT, 10) || 8888;
const host = process.env.NODE_HOST || '0.0.0.0';
const dev = process.env.NODE_ENV === 'development';
const dir = '.';

start({ dir, dev }, port, host)
    .then(async (app) => {
        // eslint-disable-next-line no-console
        console.log(`started server on ${host}:${port}`);
        await app.prepare();
    })
    .catch((err) => {
        console.error(err);
        process.exit(1);
    });

tsconfig.server.json

{
    "extends": "./tsconfig.json",
    "compilerOptions": {
        "module": "commonjs",
        "target": "es2017",
        "isolatedModules": false,
        "noEmit": false
    },
    "include": ["app.ts"]
}