Summary - async/await
- Node.js course
- Beginner
- Lesson 99/116
- 5 min
Combine async/await and Promise.all to write a file processor.
Summary - async/await
In this group you learned the async/await syntax. async functions always return a Promise; await lets you wait for a Promise's result in a synchronous-looking way. You catch errors with try/catch.
For parallel work you use await Promise.all([...]); for sequential dependent work you write consecutive await calls. Choosing the right approach shapes both readability and speed. async/await offers a flatter flow than then chains.
Practice Your turn: get a value with await
Define async function run(). Write const v = await Promise.resolve("done"). Log it with console.log(v). Call run().
Starter code
// Define async function run
// Get the value with await Promise.resolve, log with console.log
// Finally call runSample solution
async function run() {
const v = await Promise.resolve("done");
console.log(v);
}
run();Expected output
done
Practice Your turn: try/catch with await
Define async function run(). Inside a try block, write const v = await Promise.reject(new Error("error")). Inside catch (err), write console.log(err.message). Call run().
Starter code
// Define async function run
// try: await Promise.reject; catch: console.log(err.message)
// Finally call runSample solution
async function run() {
try {
const v = await Promise.reject(new Error("error"));
} catch (err) {
console.log(err.message);
}
}
run();Expected output
error
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 async/await parts
| Term | Meaning |
|---|---|
async |
returns a Promise |
await |
waits for result |
try/catch |
catches errors |
2 What does a returned value become in an async function?
- It throws an error
- It is returned as is
- It becomes undefined
- It is wrapped in a Promise Correct answer
Explanation: An async function's return value is wrapped in a Promise.