title: Node, React, with concurrently, EADDRINUSE :::8000 error
body: <p>I'm trying to use the NPM package <code>concurrently</code> with a Node/Express server on the backend, and running <code>create-react-app</code>'s server on the front end. Here is the <code>package.json</code> script:</p>
  
  <pre><code>"scripts": {
  "start": "node index.js",
  "server": "nodemon index.js",
  "client": "yarn start --prefix client",
  "dev": "concurrently \"yarn server\" \"yarn client\""
  },
  </code></pre>
  
  <p>When I execute <code>yarn dev</code> I get the following error:</p>
  
  <pre><code>$ concurrently "yarn server" "yarn client"
  $ nodemon index.js
  $ yarn start --prefix client
  [0] [nodemon] 1.17.5
  [0] [nodemon] to restart at any time, enter `rs`
  [0] [nodemon] watching: *.*
  [0] [nodemon] starting `node index.js`
  $ node index.js --prefix client
  [1] events.js:183
  [1]       throw er; // Unhandled 'error' event
  [1]       ^
  [1]
  [1] Error: listen EADDRINUSE :::8000
  [1]     at Object._errnoException (util.js:1022:11)
  [1]     at _exceptionWithHostPort (util.js:1044:20)
  [1]     at Server.setupListenHandle [as _listen2] (net.js:1367:14)
  [1]     at listenInCluster (net.js:1408:12)
  [1]     at Server.listen (net.js:1492:7)
  [1]     at Function.listen
  ...
  error Command failed with exit code 1.
  info Visit https://yarnpkg.com/en/docs/cli/run for documentation about 
  this command.
  error Command failed with exit code 1.
  info Visit https://yarnpkg.com/en/docs/cli/run for documentation about 
  this command.
  </code></pre>
  
  <p>When I use <code>lsof -i tcp:8000</code> it returns nothing. I don't know what else to do. All help is appreciated.</p>
  
  <p>Here is the server code:</p>
  
  <pre><code>const express = require('express');
  const mongoose = require('mongoose');
  const keys = require('./config/keys');
  const cookieSession = require('cookie-session');
  const passport = require('passport');
  require('./models/User');
  require('./services/passport');
  
  mongoose.connect(keys.mongoURI);
  
  const app = express();
  
  // enable cookies
  app.use(
    cookieSession({
      // cookie good for 30 days
      maxAge: 30 * 24 * 60 * 60 * 1000,
      // authenticate cookie
      keys: [keys.cookieKey]
    })
  );
  // tell passport to use cookies
  app.use(passport.initialize());
  app.use(passport.session());
  
  // get the routes
  require('./routes/authRoutes')(app);
  
  const PORT = process.env.PORT || 5000;
  app.listen(PORT);
  </code></pre>
  
  <p>No matter what I change the PORT to, it gives the same error for that port.</p>