Nextjs API routes

• can be deployed as serverless functions.
• create function inside pages/api with the following format:

// req = HTTP incoming message, res = HTTP server response
export default function handler(req, res) {
  // ...
}

• req is an instance of http.IncomingMessage, plus some pre-built middlewares.
• res is an instance of http.ServerResponse, plus some helper functions.

don't fetch an api route with getStaticProps or getServerSideProps

• do not fetch an api route from getStaticProps() or getServerSideProps(). Instead, write your server-side code directly in getStaticProps or getStaticPaths (or call a helper function).
  Here’s why: getStaticProps and getStaticPaths run only on the server-side and will never run on the client-side. Moreover, these functions will not be included in the JS bundle for the browser. That means you can write code such as direct database queries without sending them to browsers

A Good Use Case: Handling Form Input

A good use case for API Routes is handling form input. For example, you can create a form on your page and have it send a POST request to your API Route. You can then write code to directly save it to your database. The API Route code will not be part of your client bundle, so you can safely write server-side code.

export default function handler(req, res) {
  const email = req.body.email;
  // Then save email to your database, etc...
}

Preview Mode

Static Generation is useful when your pages fetch data from a headless CMS. However, it’s not ideal when you’re writing a draft on your headless CMS and want to preview the draft immediately on your page. You’d want Next.js to render these pages at request time instead of build time and fetch the draft content instead of the published content. You’d want Next.js to bypass Static Generation only for this specific case.

Next.js has a feature called Preview Mode to solve the problem above, and it utilizes API Routes. To learn more about it take a look at our Preview Mode documentation.

dynamic API routes

• API routes can be dynamic: https://nextjs.org/docs/api-routes/dynamic-api-routes