function createApp()

in packages/create-react-app/createReactApp.js [235:331]

• 84 lines of code
• 15 McCabe index (conditional complexity)

function createApp(name, verbose, version, template, useYarn, usePnp) {
  const unsupportedNodeVersion = !semver.satisfies(
    // Coerce strings with metadata (i.e. `15.0.0-nightly`).
    semver.coerce(process.version),
    '>=14'
  );

  if (unsupportedNodeVersion) {
    console.log(
      chalk.yellow(
        `You are using Node ${process.version} so the project will be bootstrapped with an old unsupported version of tools.\n\n` +
          `Please update to Node 14 or higher for a better, fully supported experience.\n`
      )
    );
    // Fall back to latest supported react-scripts on Node 4
    version = 'react-scripts@0.9.x';
  }

  const root = path.resolve(name);
  const appName = path.basename(root);

  checkAppName(appName);
  fs.ensureDirSync(name);
  if (!isSafeToCreateProjectIn(root, name)) {
    process.exit(1);
  }
  console.log();

  console.log(`Creating a new React app in ${chalk.green(root)}.`);
  console.log();

  const packageJson = {
    name: appName,
    version: '0.1.0',
    private: true,
  };
  fs.writeFileSync(
    path.join(root, 'package.json'),
    JSON.stringify(packageJson, null, 2) + os.EOL
  );

  const originalDirectory = process.cwd();
  process.chdir(root);
  if (!useYarn && !checkThatNpmCanReadCwd()) {
    process.exit(1);
  }

  if (!useYarn) {
    const npmInfo = checkNpmVersion();
    if (!npmInfo.hasMinNpm) {
      if (npmInfo.npmVersion) {
        console.log(
          chalk.yellow(
            `You are using npm ${npmInfo.npmVersion} so the project will be bootstrapped with an old unsupported version of tools.\n\n` +
              `Please update to npm 6 or higher for a better, fully supported experience.\n`
          )
        );
      }
      // Fall back to latest supported react-scripts for npm 3
      version = 'react-scripts@0.9.x';
    }
  } else if (usePnp) {
    const yarnInfo = checkYarnVersion();
    if (yarnInfo.yarnVersion) {
      if (!yarnInfo.hasMinYarnPnp) {
        console.log(
          chalk.yellow(
            `You are using Yarn ${yarnInfo.yarnVersion} together with the --use-pnp flag, but Plug'n'Play is only supported starting from the 1.12 release.\n\n` +
              `Please update to Yarn 1.12 or higher for a better, fully supported experience.\n`
          )
        );
        // 1.11 had an issue with webpack-dev-middleware, so better not use PnP with it (never reached stable, but still)
        usePnp = false;
      }
      if (!yarnInfo.hasMaxYarnPnp) {
        console.log(
          chalk.yellow(
            'The --use-pnp flag is no longer necessary with yarn 2 and will be deprecated and removed in a future release.\n'
          )
        );
        // 2 supports PnP by default and breaks when trying to use the flag
        usePnp = false;
      }
    }
  }

  run(
    root,
    appName,
    version,
    verbose,
    originalDirectory,
    template,
    useYarn,
    usePnp
  );
}