---
id: 673407d56c3dce67fa97969b
title: What Is Async/Await, and How Does It Work?
challengeType: 19
dashedName: what-is-async-await-and-how-does-it-work
---

# --interactive--

In the previous lessons, you learned about asynchronous programming which allows other code to run while we wait for some time-consuming tasks to complete, like fetching data from a server, reading data from a file, and so on.

`async`/`await`, built on top of promises, makes writing and reading asynchronous code easier. When you put the `async` keyword before a function, it means that function will always return a `Promise`. The `await` keyword, which allows you to wait for a `Promise` to resolve before moving on to the next line of code, can only be used inside of asynchronous functions or the top level bodies of modules. Here's an example to illustrate how `async`/`await` works:

:::interactive_editor

```js
async function delayedGreeting(name) {
  console.log("A Messenger entered the chat...");
  await new Promise(resolve => setTimeout(resolve, 2000));
  console.log(`Hello, ${name}!`);
}

delayedGreeting("Alice");
console.log("First Printed Message!");
```

:::

In this code, we define an `async` function called `delayedGreeting`. Inside this function, we use `await` to pause the execution for 2 seconds. After the delay, it prints a greeting. 

When we call this function, you'll see `First Printed Message!` appear before the greeting. This is because the function is asynchronous - it doesn't block the rest of the code from running.

One of the biggest advantages of `async`/`await` is error handling. With promises, we often had to use `.catch()` method to handle errors. With `async`/`await`, we can use `try`/`catch` blocks. Here's an example:

```js
async function fetchUserData() {
  try {
    let response = await fetch(`https://api.example.com/users`);
    let userData = await response.json();
    console.log(userData);
  } catch (error) {
    console.log("Error fetching user data:", error);
  }
}

fetchUserData();
```

In this example, we're using `async`/`await` to fetch user data from an API. The `await` keyword is used twice: once to wait for the fetch operation to complete, and again to wait for the JSON parsing to finish. If any error occurs during this process, it will be caught in the `catch` block.

# --questions--

## --text--

What is the primary purpose of the `async` keyword in JavaScript?

## --answers--

To make a function run faster.

### --feedback--

Think about what `async` does to the function's return value.

---

To indicate that a function will always return a Promise.

---

To create a new thread for the function to run on.

### --feedback--

Think about what `async` does to the function's return value.

---

To prevent a function from being called asynchronously.

### --feedback--

Think about what `async` does to the function's return value.

## --video-solution--

2

## --text--

Where can the `await` keyword be used in JavaScript?

## --answers--

Anywhere in the code.

### --feedback--

Consider the restrictions on where `await` can be placed.

---

At the very beginning of your code.

### --feedback--

Consider the restrictions on where `await` can be placed.

---

Inside `async` functions.

---

Only in `try...catch` blocks.

### --feedback--

Consider the restrictions on where `await` can be placed.

## --video-solution--

3

## --text--

What happens when an error occurs in an awaited Promise?

## --answers--

The program crashes.

### --feedback--

Think about how error handling works with `async`/`await`.

---

The error is automatically logged to the console.

### --feedback--

Think about how error handling works with `async`/`await`.

---

Nothing, errors in Promises are ignored.

### --feedback--

Think about how error handling works with `async`/`await`.

---

The error can be caught using a `try...catch` block.

## --video-solution--

4