Function isYarnUsed

src/util.ts:139–144

(existsSync = fs.existsSync)

 * - If only package-lock.json or both exist, use npm
 */
export function isYarnUsed(existsSync = fs.existsSync): boolean {
  if (existsSync('package-lock.json')) {
    return false;
  }
  return existsSync('yarn.lock');
}

export function getPkgManagerCommand(isYarnUsed?: boolean): string {
  return (