Next.js Hot Content Reload

When working locally, the "Hot Content Reload" lets you "hot reload" the props returned by Next.js getStaticProps and getServerSideProps methods.

The idea is similar to Webpack's Hot Module Replacement. However, instead of watching for code changes and replacing the changed components in the browser, it lets you configure your Next.js site to watch for content changes made in Headless CMS or local files and update the page with the new content without refreshing the browser.

How to use

The Hot Content Reload consists of two parts:

1. A server with a websocket exposing the notifyPropsChanged function. When you call this function, it sends a websocket event to the client, causing it to reload the props of the currently rendered page.
2. A high-order component that wraps the page component. It listens to the websocket events sent by the server and reloads the props when such events are received.

To create the websocket server import the startHotContentReloadSocketServer function from the @stackbit/nextjs-hot-content-reload package inside your next.config.js. Create the socket server by invoking the startHotContentReloadSocketServer() function. Make sure to do that when running next.js in development mode. Then call the socketServer.notifyPropsChanged() method whenever the props driving your pages are changed. See the following section for examples of when to call this method when working with different headless CMS.

next.config.js:

const { startHotContentReloadSocketServer } = require('@stackbit/nextjs-hot-content-reload');

if (process.env.NODE_ENV === 'development') {
    // You can also provide optional options object with custom "port", "namespace" and "eventName"
    // or leave it empty to use defaults that work with Stackbit preview.
    const socketServer = startHotContentReloadSocketServer({
        // port: '...',
        // namespace: '...',
        // eventName: '...'
    });

    // call socketServer.notifyPropsChanged() when content is changed
    function onContentChange() {
        socketServer.notifyPropsChanged();
    }
}

module.exports = {
    // ... next.js config goes here
};

Next, wrap your page components with withHotContentReload high-order-component to enable hot-content-reload in these pages. By default, withHotContentReload sets websocket listener when process.env.NODE_ENV === 'development'. If you need to customize the behavior of withHotContentReload high-order-component, import the hotContentReload factory method and pass it custom options to create your own withHotContentReload HOC.

import { withHotContentReload } from '@stackbit/nextjs-hot-content-reload/hotContentReload';

function Page(props) {
    return (
        <main>{props.title}</main>
    );
}

export default withHotContentReload(Page);

export function getStaticProps() {
    // ...
}

Examples

Hot reloading file-system content

Assuming your site's pages render data stored in markdown files, you can use chokidar to listen for file changes and call socketServer.notifyPropsChanged():

const { startHotContentReloadSocketServer } = require('@stackbit/nextjs-hot-content-reload');
const chokidar = require('chokidar');

if (process.env.NODE_ENV === 'development') {
    const socketServer = startHotContentReloadSocketServer();

    function onContentChange(filePath) {
        socketServer.notifyPropsChanged();
    }

    const watcher = chokidar.watch('content', {ignoreInitial: true});
    watcher.on('add', onContentChange);
    watcher.on('change', onContentChange);
    watcher.on('unlink', onContentChange);
}

Contentful

If your site uses Contentful as its headless CMS, you can use the @stackbit/contentful-listener package. Call the socketServer.notifyPropsChanged() when contentful-listener notifies you of a content change:

const { startHotContentReloadSocketServer } = require('@stackbit/nextjs-hot-content-reload');
const { ContentfulListener } = require('@stackbit/contentful-listener');

if (process.env.NODE_ENV === 'development') {
    const socketServer = startHotContentReloadSocketServer();

    const contentfulListener = new ContentfulListener({
        spaceId: process.env.CONTENTFUL_SPACE_ID,
        accessToken: process.env.CONTENTFUL_PREVIEW_API_KEY,
        environment: 'master',
        host: 'preview.contentful.com',
        pollingIntervalMs: 1000,
        callback: (result: CallbackResponse) => {
            socketServer.notifyPropsChanged();
        }
    });
    contentfulListener.start();
}

Sanity

If your site uses Sanity as its headless CMS, you can use the @sanity/client package and its listen API and call the socketServer.notifyPropsChanged() when Sanity notifies you of change events:

const { startHotContentReloadSocketServer } = require('@stackbit/nextjs-hot-content-reload');
const sanityClient = require('@sanity/client');

if (process.env.NODE_ENV === 'development') {
    const socketServer = startHotContentReloadSocketServer();
    const client = sanityClient({
        projectId: 'your-project-id',
        dataset: 'dataset-name',
        apiVersion: '2021-03-25', // use current UTC date - see "specifying API version"!
        token: 'sanity-auth-token', // or leave blank for unauthenticated usage
        useCdn: false
    });

    const query = '*[!(_id in path("_.**"))]';
    const params = {};

    const subscription = client.listen(query, params).subscribe((update) => {
        socketServer.notifyPropsChanged();
    });
}

Example Project

You can find an example Next.js starter project inside the example folder.

There you will find pages/index.js file that implements getStaticProps method. The getStaticProps method loads data from content/index.yaml and returns as props to be consumed by the Home component. It also wraps the Home component with hotContentReload high-order component to setup websocket listener on the client as described before.

function Home(props) {
    // ...
}

const withHotContentReload = hotContentReload();

export default withHotContentReload(Home);

export function getStaticProps() {
    const yamlData = fs.readFileSync('content/index.yaml', 'utf-8')
    const props = yaml.load(yamlData)
    return {props}
}

And finally, next.config.js installs a websocket service and a file listener that calls socketServer.notifyPropsChanged() when the content/index.yaml file is changed.

To try it out:

• clone this repo
• run npm install in the root folder
• run npm run build in the root folder
• run cd example
• run npm install
• run npm run dev
• navigate to http://localhost:3000
• open the content/index.yaml file and change something
• the browser will instantly reflect the changes