Async/Await Deep Dive (JavaScript)

Use these notes to explain how async/await works under the hood.

Key mechanics

• async functions return a Promise.
• await pauses execution and resumes on microtask completion.
• Errors in awaited promises throw like synchronous errors.

const load = async () => {
  const res = await fetch('/api/data');
  if (!res.ok) throw new Error('bad response');
  return res.json();
};

Event loop notes

• Microtasks run before the next macrotask.
• Avoid blocking the main thread with heavy CPU work.

Cancellation

• Use AbortController for fetch and other DOM APIs.

Interview prompt

• Explain the ordering of Promise.resolve, queueMicrotask, and setTimeout.