Cant load a react app after starting server

This is a deprecation warning, meaning that you need to start using the newly suggested way of configuring your middleware. Instead of onBeforeSetupMiddleware and onAfterSetupMiddleware, use the setupMiddlewares-property.

The documentation itself can be found on Webpack's website (in this case here: https://webpack.js.org/configuration/dev-server/#devserversetupmiddlewares)

The configuration will look something like this (coming from onBeforeSetupMiddleware and onAfterSetupMiddleware):

setupMiddlewares: (middlewares, devServer) => {
    middleware1(devServer.app)
    middleware2(devServer.app)

    return middlewares
},

Another useful way of fixing this issue is by looking at the code others have written to fix this issue. I found this example to be helpful: https://github.com/facebook/docusaurus/pull/6168

I had the same issue. The problem was with the setupProxy.js.

If your setupProxy.js files look like below

const proxy = require('http-proxy-middleware');

module.exports = function(app) {
  app.use(proxy('/proxypath', { target: '<target path>' }));
};

Change it as below

const { createProxyMiddleware } = require('http-proxy-middleware');

module.exports = function(app) {
  app.use(createProxyMiddleware('/proxypath', { target: '<target path>' }));
};

As in the error, you have quoted, onAfterSetupMiddleware and onBeforeSetupMiddleware have been deprecated therefore the proxy method is not working as expected. So when you start the server with npm start the browser tries to redirect to the proxy URL. That's why you see as the react app is not loading.

I had the same error.

An authentication middleware, in my case AWS Amplify Auth, was changed incorrectly and my webpack config yielded an error. The fix for me was to re-install clean then debug the error.

So delete package-lock.json, delete the node-modules folder, and reinstall with "npm i".

Although this does not get to the root of the issue it should work to at least bring up the Dev Server to view any errors.

It's just a deprecation warning from one of the libraries you used within the app, have you tried to open http://localhost:3000 on your local? it is supposed to be running fine

In file: node_modules/react-scripts/config/webpackDevServer.config.js

like this

onBeforeSetupMiddleware(devServer) {
    // Keep `evalSourceMapMiddleware`
    // middlewares before `redirectServedPath` otherwise will not have any effect
    // This lets us fetch source contents from webpack for the error overlay
    devServer.app.use(evalSourceMapMiddleware(devServer));

    if (fs.existsSync(paths.proxySetup)) {
    // This registers user provided middleware for proxy reasons
    require(paths.proxySetup)(devServer.app);
    }
},
onAfterSetupMiddleware(devServer) {
    // Redirect to `PUBLIC_URL` or `homepage` from `package.json` if url not match
    devServer.app.use(redirectServedPath(paths.publicUrlOrPath));

    // This service worker file is effectively a 'no-op' that will reset any
    // previous service worker registered for the same host:port combination.
    // We do this in development to avoid hitting the production cache if
    // it used the same host and port.
    // https://github.com/facebook/create-react-app/issues/2272#issuecomment-302832432
    devServer.app.use(noopServiceWorkerMiddleware(paths.publicUrlOrPath));
},

change to

setupMiddlewares: (middlewares, devServer) => {
    if (!devServer) {
        throw new Error('webpack-dev-server is not defined')
    }

    if (fs.existsSync(paths.proxySetup)) {
        require(paths.proxySetup)(devServer.app)
    }

    middlewares.push(
        evalSourceMapMiddleware(devServer),
        redirectServedPath(paths.publicUrlOrPath),
        noopServiceWorkerMiddleware(paths.publicUrlOrPath)
    )

    return middlewares;
},

Tried changing the names in webpackDevServer.config.js it worked for me.

1. Open node_modules folder.
2. Search for webpackDevServer.config.js.
3. Open the js file and edit it.

I had a similar behaviour. Running the react scripts and then being stuck at the "Starting the development server...". Although it run via "react-app-rewired" I guess this is some general thing with react-scripts.

I updated an existing project from react-scripts 4.0.3 to 5. That was my cause. I tried a lot of things but unfortunately nothing helped. I could not move forward and reverted the upgrade to the v5 of react-scripts.

Maybe this helps someone.

What fixed it for me was running npm i webpack-dev-middleware.