Concurrency vs. Parallelism

Concurrency vs. Parallelism

In this lesson — part of Concurrency Basics — you'll learn concurrency vs. parallelism in JavaScript and why it matters in real work.

Why it matters

Modern programs wait on networks and disks — async lets them stay responsive.

Key ideas

• Blocking vs. non-blocking
• Callbacks, promises, async/await
• Concurrency vs. parallelism
• Error handling in async code

In practice

Here's how it looks in idiomatic JavaScript:

async function fetchUser(id) {
  const res = await fetch(`https://api.example.com/users/${id}`);
  if (!res.ok) throw new Error(`HTTP ${res.status}`);
  return res.json();
}
fetchUser(1).then(user => console.log(user));

JavaScript note: async/await is syntactic sugar over Promises: await pauses the function until the Promise settles without blocking the single-threaded event loop.

Try it yourself

Exercise: In JavaScript, fetch two things concurrently and combine the results.

Recap

You now understand concurrency vs. parallelism and can apply it in JavaScript. Mark this lesson complete and continue to the next one.