how to create react js build code example

Example 1: react build command

npm run build

Example 2: build react app

Build a react project
Code has to be bundled using a bundler like webpack and
 transformed using a compiler like Babel.
do production optimizations such as code splitting(critical CSS)
statically pre-render some pages for performance and SEO. 
use server-side rendering or client-side rendering.
write some server-side code to connect your React app to your data store.
OR use create-react-app