Next.js run function/script when starting app

Question

I have a (server-side) function I'd like to run when first starting my next.js server. Ordinarily I'd do something like this in my package.json script definition: node./path/to/script.js && next start . But the script in question imports several resources from "webpacked" code, so that's not so easy. (I know it's possible to turn on es6 support in node.js with --experimental-modules , but this brings its own problems and I'd rather not go down that rabbit hole)

The best solution I have so far is to create an api endpoint to run these scripts and then either manually hit that endpoint after starting. But it seems like such a hack to do this, and it's possible that this endpoint could be used in some sort of DoS attack if someone found it.

Is there a better solution, something that just allows one to register a function/callback to be run when the app is starting? I figured a likely place would be the next.config.js but I don't see anything likely in the list of possible settings.

Answer 1

I guess you could use the webpack configuration on the next.config file to register a new plugin and run it after the build is done.

module.exports = {
    webpack: (config, options) => {
        config.plugins.push(
            {
                apply: (compiler) => {
                    compiler.hooks.afterEmit.tap('AfterEmitPlugin', (compilation) => {
                        console.log(".. Run after build")
                    });
                }
            }    
        )
        return config
    },
}

Answer 2

Could it be possible to run the api after entering the code?

_app.js

const MyApp({pageProps}) {
   useEffect(() => {
   /* call to run API on app mount */
      return ( /* Call to clean up after app unmounted*/);
   },[])

   return (
      <Component {...pageProps} />
   );
}
export default MyApp;

Another solution could be using a Next's getServerSideProps or getStaticProps on the index/entry point for the app

index.js

export default function foo({props}) {
   /* Do something */
   return( /* return something to renderer */);
}

export function getServerSideProps() {
   const caller = fetch(/* Return from running API endpoint*/)
   return (
      props: caller;
   )
}

both of the get* functions from Next.js will run before the component renders to ensure that the data has been fetched. They are used for data fetching, but I don't see why they couldn't be used as a hack to force the API to run near launch.

Answer 3

The only solution I've found for the end of 2022, is using some bash scripts. It's actually simple. Original bash answer My dev script:

start_dev.sh

yarn run dev & curl -I http://localhost:3002 & wait

My production script:

start.sh

yarn run start & curl -I http://localhost:3000 & wait

Here, I use curl to peek my site. That causes the site to actually launch it's scripts that normally launch on first visit. For sure, you can place you startup scripts anywhere you want, using home page is not required.

In my case, I need some database preparing and page data caching. So I use NextConnect for that. Here I give one example (I have simular code for each page and api route):

export async function getServerSideProps({ req, res }) {
    const middlewares = NextConnect().use(waitDB).use(withUser).use(withPagesCache)
    await middlewares.run(req, res);
    ...
}

My withUser middleware:

export default async function (req, res, next) {
  let cookies = getCookies({ req, res });
  let { user_id, token } = cookies;
  // some logic. You are free to use your globals, your DB and so on.
  console.log("Test this middleware");

  next();
}