server.js

const express = require('express');
const bodyParser = require('body-parser');
const methodOverride = require('method-override');
const path = require('path');
const app = express();

// Middleware
app.use(bodyParser.json());
app.use(methodOverride('_method'));
app.use(express.urlencoded({ extended: true }));


app.use(function (req, res, next) {

  // Website you wish to allow to connect
  res.setHeader('Access-Control-Allow-Origin', 'http://localhost:3000');

  // Request methods you wish to allow
  res.setHeader('Access-Control-Allow-Methods', 'GET, POST, OPTIONS, PUT, PATCH, DELETE');

  // Request headers you wish to allow
  res.setHeader('Access-Control-Allow-Headers', 'X-Requested-With,content-type');

  // Set to true if you need the website to include cookies in the requests sent
  // to the API (e.g. in case you use sessions)
  res.setHeader('Access-Control-Allow-Credentials', true);

  // Pass to next layer of middleware
  next();
});

// Use Routes
app.use('/api/items', require('./routes/api/items'));
app.use('/api/comments', require('./routes/api/comments'));

if (process.env.NODE_ENV === 'production') {
  // Set static folder
  app.use(express.static('client/build'));

  app.get('*', (req, res) => {
    res.sendFile(path.resolve(__dirname, 'client/build/index.html'));
  });
}

const port = process.env.PORT || 5002;

app.listen(port, () => console.log(`Server started on port ${port}`));