build react-node-express project using yarn

instructor.js

// In React JS project go to package.json
// Inside the 'scripts' block, change
"start":"react-scripts start"
// to
"start":"react-scripts build && (cd backend && yarn start)",
// in which, backen is the root directory of node-express app
// and add
"start-client": "react-scripts start",  //starts react app on port=3000

// now in node-express root directory, open server.js (maybe app.js)
// make this changes
const path = require('path');
app.use(express.static(path.join(__dirname, "..", "build")));