in packages/react-scripts/config/webpackDevServer.config.js [112:122]
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);
}
},