[yarn with npm fallback] Try to install dependencies using yarn or fall back to npm if yarn is not available #nodejs #yarn #npm

yarn-or-npmi.js

const os = require('os');
const exec = require('child_process').exec;

switch (os.platform()) {
  case 'win32':
    exec('yarn --version', (err, stdout, stderr) => {
      if (err) {
        exec('npm install');
        return;
      } else {
        exec('yarn');
      }
    });

    break;
  case 'darwin':
  case 'linux':
    exec('if [ -z `which yarn`]; then npm install; else yarn; fi;');
    break;
  default:
    throw new Error('Unsupported platform.');
}

Or use yarn || npm install. Should work on both, Windows and macOS

Use to run the command following || only if the command preceding || fails. Cmd.exe runs the first command, and then runs the second command only if the first command did not complete successfully (receives an error code greater than zero).
~ Command shell overview