Promises & Async/Await

// Promises
function fetchUser(id) {
  return new Promise((resolve, reject) => {
    // Simulate an API call
    setTimeout(() => {
      if (id > 0) {
        resolve({ id, name: "Alice" });
      } else {
        reject(new Error("Invalid user ID"));
      }
    }, 100);
  });
}

// .then() chaining
fetchUser(1)
  .then(user => {
    console.log(user.name);  // Alice
    return fetchUser(2);     // chain another promise
  })
  .then(user => console.log(user))
  .catch(err => console.error(err.message));

// async/await — cleaner syntax for the same thing
async function getUser() {
  try {
    const user = await fetchUser(1);
    console.log(user.name);   // Alice
  } catch (err) {
    console.error(err.message);
  }
}

getUser();

// fetch() — built-in for HTTP requests
async function getGitHubUser(username) {
  const response = await fetch(`https://api.github.com/users/${username}`);

  if (!response.ok) {
    throw new Error(`HTTP error: ${response.status}`);
  }

  const data = await response.json();
  return data;
}

async function main() {
  try {
    const user = await getGitHubUser("torvalds");
    console.log(user.name);         // Linus Torvalds
    console.log(user.public_repos); // lots
  } catch (err) {
    console.error("Failed:", err.message);
  }
}

main();

// Run multiple promises in parallel
async function fetchAll() {
  const [user1, user2] = await Promise.all([
    getGitHubUser("torvalds"),
    getGitHubUser("gvanrossum"),
  ]);
  console.log(user1.name, user2.name);
}