command

mkdir react-number-game
cd react-number-game
npm init -y
npm i parcel-bundler --save-dev
npm i react react-dom @types/react @types/react-dom
mkdir src

index.html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>React TypeScript App</title>
</head>
<body>
  <div id="root"></div>
  <script src="./index.tsx"></script>
</body>
</html>

index.tsx

import * as React from 'react'
import { Component } from 'react'
import { render } from 'react-dom'
// import './index.css'

class App extends Component {
  render() {
    return (<h1>Hello World!</h1>)
  }
}

render(<App />, document.getElementById('root'))

package.json

"scripts": {
    "start": "parcel src/index.html",
    "build": "parcel build src/index.html",
    "clean": "rimraf dist/index.html dist/src.*.css dist/src.*.js dist/src.*.map",
    "predeploy": "npm run clean -s && npm run build -s",
    "deploy": "gh-pages -d dist"
  },

Reference

Bootstrapping a React TypeScript project with Parcel