force react to run in 80 instead of 3000 code example

Example: set port in react app

//in package.json

"start": "react-scripts start"
t0
//linux
"start": "PORT=3006 react-scripts start"
or 
"start": "export PORT=3006 react-scripts start"
//windows
"start": "set PORT=3006 && react-scripts start"