const promise = new Promise((resolve, reject) => {
  setTimeout(() => {
    const success = true;
    success ? resolve('Done!') : reject('Failed');
  }, 1000);
});

promise
  .then(result => console.log(result))
  .catch(error => console.error(error));

• A promise is always in one of three states: pending, fulfilled or rejected
• Once settled (fulfilled/rejected), a promise's outcome never changes
• .then() registers success handlers; .catch() registers error handlers
• .finally() runs regardless of outcome — great for cleanup