Promises & Async/Await

What is a Promise?

A Promise is an object representing the eventual result (or failure) of an asynchronous operation.

3 States of a Promise

• Pending - Waiting for result
• Fulfilled - Succeeded with a value
• Rejected - Failed with an error

Examples

Creating a Promise

const fetchData = () => {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve({ id: 1, name: 'Notex' });
    }, 1000);
  });
};

Async/Await

async function getData() {
  try {
    const data = await fetchData();
    console.log(data);
  } catch (error) {
    console.error('Error:', error);
  }
}

Promise.all - Run in Parallel

const [users, posts] = await Promise.all([
  fetchUsers(),
  fetchPosts(),
]);

Pattern Comparison

Pattern	Pros	Cons
Callbacks	Simple	Callback hell
Promises	Chainable	Verbose
Async/Await	Readable	Needs try/catch