title: Why does React have a server on its own?
body: <p>First of all, I know the question is badly formulated. I can't think of any thing to describe the situation as I'm a beginner.
  So when on cmd we type <code>npx create-react-app myapp</code>, this sets up the react project. Then we could do <code>npm start</code> and we could view the react app on <code>localhost:3000</code>. I wish to know why it is so. The react app is on client side, so why does it need a server? Next, I want to set up a node js server and does it need to use the same port as the react app? My guts says no. Briefly, I wish to know why react use <code>localhost:3000</code> when it is client-side.
  Thanks in advance</p>