By the end of this lesson
Await a promise and catch a rejected asynchronous operation.
Before you start
- Node.js 24 with a terminal and plain-text editor; the browser-only lesson is labelled separately.
- Complete lesson 16 or be comfortable with its examples.
Three words to know
- Promise
- An object representing a future completion or failure.
- async function
- A function that always returns a promise.
- await
- Pause the current async flow until a promise settles.
1. An async result is still a promise
Even returning a plain value from an async function produces a fulfilled promise. await unwraps its result for the current flow. Our .mjs source allows top-level await. Other work is not magically made synchronous by awaiting one operation.
async function describeCount(count) {
return `records: ${count}`;
}
const pending = describeCount(3);
console.log(pending instanceof Promise);
console.log(await pending);
What you should see · example output
true records: 3
2. Catch the rejection where you await it
A rejection behaves like a thrown error when awaited. Forgetting await may let the surrounding try finish before the error occurs. Always decide who observes a promise’s failure; do not rely on an unhandled rejection as an application error strategy.
async function loadPracticeData() {
throw new Error("Practice data unavailable");
}
try {
await loadPracticeData();
} catch (error) {
console.log(error.message);
}
What you should see · example output
Practice data unavailable
3. Concurrency needs its own contract
Promise.all can combine independent tasks, but it is not a request-rate limiter and does not cancel every other operation when one rejects. The course examples make no network requests. A later HTTP tool would need explicit timeouts, concurrency limits, cancellation and response validation, not just an async keyword.
YOUR TURN
A small check before you continue
Does an async function returning 4 return the number 4 directly? What obtains the fulfilled value?
Show a suggested answer
It returns a promise fulfilled with 4. await gets the value within an allowed async context, or a then callback observes it.
Sources and scope
Documentation and examples reviewed 2026-10-18. Provider screens, package versions and output wording can differ. Examples show expected outcomes; they are not a claim that OpenViST connected to your server or verified your setup.