How do async and await work, and how do you handle errors?

async and await are syntax over promises. They make asynchronous code read sequentially without changing the underlying event-loop behaviour.

async function loadUser(id) {
  try {
    const response = await fetch("/api/users/" + id);

    if (!response.ok) {
      throw new Error("HTTP " + response.status);
    }

    return await response.json();
  } catch (error) {
    console.error(error);
    throw error;
  }
}

What await actually does

• It pauses the current async function, not the whole thread
• Other code and other tasks continue while the promise is pending
• The function resumes in a microtask after the promise settles
• A resolved value is returned; a rejection is thrown at the await line

Independent awaits run sequentially. If two requests do not depend on each other, start both and await them together with Promise.all.

const [user, posts] = await Promise.all([
  fetch("/api/user").then((response) => response.json()),
  fetch("/api/posts").then((response) => response.json()),
]);

Do not pass an async callback to forEach and expect it to wait. forEach ignores the returned promises. Use for...of for sequential work or Promise.all with map for parallel work.