JavaScript await keyword

last modified April 16, 2025

In this article we show how to work with asynchronous operations using the await keyword in JavaScript.

The await keyword

The await keyword is used to pause the execution of an async function until a Promise is resolved. It can only be used inside async functions. This makes asynchronous code look and behave more like synchronous code.

When await is used, it waits for the Promise to settle. If the Promise resolves, it returns the resolved value. If rejected, it throws the rejection value. This simplifies working with Promises and avoids callback hell.

The await keyword is always used with Promises. It makes asynchronous code more readable and maintainable. Error handling can be done with try/catch blocks, similar to synchronous code.

Basic await example

The following example demonstrates the basic usage of the await keyword with a simple Promise.

async function fetchData() {
 const data = await new Promise((resolve) => {
 setTimeout(() => resolve('Data received'), 1000);
 });
 console.log(data);
}
fetchData();

This example creates a Promise that resolves after 1 second. The await keyword pauses execution until the Promise resolves. The resolved value is then assigned to the data variable. Finally, the value is logged to the console.

$ node main.js
Data received

Await with fetch API

The await keyword is commonly used with the Fetch API.

async function getUser() {
 const response = await fetch('https://api.github.com/users/octocat');
 const data = await response.json();
 console.log(data.name);
}
getUser();

This example fetches user data from GitHub's API. The first await waits for the fetch request to complete. The second await waits for the response to be converted to JSON. This shows how await can chain asynchronous operations cleanly.

$ node main.js
The Octocat

Error handling with try/catch

Error handling with await can be done using try/catch blocks.

async function fetchWithErrorHandling() {
 try {
 const response = await fetch('https://invalid.url');
 const data = await response.json();
 console.log(data);
 } catch (error) {
 console.error('Error:', error.message);
 }
}
fetchWithErrorHandling();

This example demonstrates error handling when a fetch request fails. The try block contains the asynchronous operations. If any Promise rejects, execution jumps to the catch block. This provides a clean way to handle errors in async code.

$ node main.js
Error: fetch failed

Await with multiple Promises

Multiple Promises can be awaited either sequentially or in parallel.

async function getMultipleData() {
 const promise1 = Promise.resolve('First');
 const promise2 = Promise.resolve('Second');
 
 const result1 = await promise1;
 const result2 = await promise2;
 
 console.log(result1, result2);
}
getMultipleData();

This example shows sequential awaiting of multiple Promises. Each await pauses execution until its Promise resolves. For parallel execution, Promise.all() would be more efficient. This demonstrates the basic pattern of awaiting multiple operations.

$ node main.js
First Second

Await with Promise.all

Promise.all() can be used with await for parallel execution.

async function fetchInParallel() {
 const urls = [
 'https://api.github.com/users/octocat',
 'https://api.github.com/users/torvalds'
 ];
 
 const promises = urls.map(url => fetch(url).then(res => res.json()));
 const results = await Promise.all(promises);
 
 results.forEach(user => console.log(user.name));
}
fetchInParallel();

This example fetches data from multiple URLs in parallel. Promise.all() waits for all Promises to resolve. The await pauses until all requests complete. This is more efficient than awaiting each request sequentially.

$ node main.js
The Octocat
Linus Torvalds

Await in top-level code

In modern JavaScript, await can be used in top-level code.

const data = await Promise.resolve('Top-level await');
console.log(data);

This example demonstrates top-level await, available in ES modules. The await keyword can be used outside async functions in module scope. This simplifies initialization code that needs to wait for async operations.

$ node main.js
Top-level await

Practical use case: file reading

Here's a practical example of using await with file operations.

import { promises as fs } from 'fs';
async function readFiles() {
 try {
 const content = await fs.readFile('example.txt', 'utf-8');
 console.log(content);
 } catch (err) {
 console.error('Error reading file:', err);
 }
}
readFiles();

This example reads a file asynchronously using Node.js fs module. The await keyword waits for the file reading operation to complete. Error handling is done with try/catch. This shows a common real-world use case for await.

$ node main.js
File content here...

Source

await - language reference

In this article we have demonstrated how to use the await keyword for asynchronous programming in JavaScript.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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