Node.js: Check if a command exists

cmd-exists.js

// returns a Promise which fulfills with the result of a shell command
// rejects with stderr
function run(command) {
  return new Promise((fulfill, reject) => {
    exec(command, (err, stdout, stderr) => {
      if (err) {
        reject(err);
        return;
      }

      if (stderr) {
        reject(new Error(stderr));
        return;
      }

      fulfill(stdout);
    });
  });
}

// returns Promise which fulfills with true if command exists
function exists(cmd) {
  return run(`which ${cmd}`).then((stdout) => {
    if (stdout.trim().length === 0) {
      // maybe an empty command was supplied?
      // are we running on Windows??
      return Promise.reject(new Error('No output'));
    }

    const rNotFound = /^[\w\-]+ not found/g;

    if (rNotFound.test(cmd)) {
      return Promise.resolve(false);
    }

    return Promise.resolve(true);
  });
}