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What are async functions in JavaScript

Async functions in JavaScript are a powerful feature that simplifies the way you write asynchronous code. Introduced in ECMAScript 2017 (ES8), async functions are a higher-level abstraction over Promises, making asynchronous code look and behave a bit more like synchronous code. This feature makes it easier to read and write promises, reducing the complexity of handling asynchronous operations.

Key Characteristics

• Simplifies Asynchronous Code: By using async and await, you can write asynchronous code that's easier to read and understand compared to traditional promise chains or callback-based approaches.
• Error Handling: Async functions use standard JavaScript try/catch blocks for error handling, making asynchronous error handling more straightforward and consistent with synchronous code.
• Returns a Promise: An async function always returns a promise. If the function returns a value, the promise will be resolved with that value. If the async function throws an error, the promise is rejected with that error.

Syntax

To define an async function, you prepend the async keyword to the function declaration:

async function myAsyncFunction() {
  // function body
}

Within an async function, you use the await keyword before a promise to wait for its resolution:

async function fetchData() {
  const data = await fetch('https://api.example.com');
  const json = await data.json();
  return json;
}

Using Async Functions

Basic Example:

async function getTodo() {
  const response = await fetch('https://jsonplaceholder.typicode.com/todos/1');
  const todo = await response.json();
  console.log(todo);
}

getTodo();

Error Handling:

You can handle errors using try-catch blocks:

async function fetchWithErrorHandling() {
  try {
    const response = await fetch('https://api.example.com/might-not-exist');
    const data = await response.json();
    console.log(data);
  } catch (error) {
    console.error("Oops, something went wrong!", error);
  }
}

fetchWithErrorHandling();

Async Arrow Functions:

You can also define async functions using the arrow function syntax:

const fetchDataAsync = async () => {
  const response = await fetch('https://api.example.com');
  const data = await response.json();
  console.log(data);
};

fetchDataAsync();

When to Use Async Functions

Async functions are particularly useful when dealing with multiple asynchronous operations that need to occur in a particular sequence. They also significantly improve the readability and maintainability of your code by allowing you to write asynchronous code that looks more like traditional synchronous, procedural code.

However, it's important to remember that async/await is syntactic sugar over Promises, and understanding how Promises work is crucial to effectively using async/await. The feature shines in scenarios where complex promise chains would otherwise be required, such as in web API calls, file operations, or any other asynchronous action that involves waiting for operations to complete before proceeding.