Summary - async/await

Build a flow that fetches data from two APIs in sequence and combines them using async/await.

async/await summary

async/await turns promise-based asynchronous code into something that looks synchronous. An async function always returns a promise; await waits for a promise's result. Errors are caught with try/catch; independent tasks run in parallel with Promise.all; async iterables are walked with for await...of.

In this summary you will build a flow that combines all of them: first two API calls in sequence, then two parallel data loads.

Exercise Two API calls in sequence

Write async function loadProfile(). Inside a try block, first call await fetchUser() and assign to user, then await fetchPosts(user.id) and assign to posts. Add a catch (err) block that logs the error with console.error(err).

Show example solution

async function loadProfile() {
  try {
    const user = await fetchUser();
    const posts = await fetchPosts(user.id);
  } catch (err) {
    console.error(err);
  }
}

Exercise Load data in parallel

Write async function loadParallel(). Inside it, call await Promise.all([fetchProfile(), fetchSettings()]) and destructure the result as [profile, settings].

Show example solution

async function loadParallel() {
  const [profile, settings] = await Promise.all([
    fetchProfile(),
    fetchSettings()
  ]);
}

Test yourself

Match async/await concepts

async function

always returns a promise
await

waits for the promise's result
try/catch

catches an async error
Promise.all

enables parallel execution
for await...of

walks an async iterable
Which one is the fastest?
```
// A: sequential
const a = await p1(); const b = await p2();
// B: parallel
const [a, b] = await Promise.all([p1(), p2()]);
```
- Option B is faster
- Option A is faster
- Both finish in equal time
- Time does not depend on the promises
Show answer

Option B is faster — Correct! Parallel execution shortens total time for independent operations.

Next lesson: fetch basics

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