import chalk from 'chalk'; import detectPort from 'detect-port'; const port = process.env.PORT || '4343'; detectPort(port, (err, availablePort) => { if (port !== String(availablePort)) { throw new Error( chalk.whiteBright.bgRed.bold( `Port "${port}" on "localhost" is already in use. Please use another port. ex: PORT=4343 yarn start` ) ); } else { process.exit(0); } });