Why async and await are needed in Javascript

Introduction

Async and await help us write code that waits for tasks to finish without stopping everything else. They make working with slow things like loading data easier and cleaner.

When you need to get data from the internet and want to wait for it before continuing.

When you want to read or write files without freezing your program.

When you have tasks that take time and you want your app to stay responsive.

When you want to handle multiple tasks one after another without messy code.

Syntax

Javascript

async function myFunction() {
  const result = await someAsyncTask();
  console.log(result);
}

async marks a function to work with asynchronous code.

await pauses the function until the task finishes, then continues.

Examples

This function returns a promise automatically because it is async.

Javascript

async function greet() {
  return 'Hello!';
}

Here, await waits for the data to load before moving on.

Javascript

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

Sample Program

This program shows how await pauses the function for 2 seconds without stopping the whole program.

Javascript

async function waitAndSay() {
  console.log('Start');
  await new Promise(resolve => setTimeout(resolve, 2000));
  console.log('Done waiting 2 seconds');
}

waitAndSay();

Important Notes

Without async and await, you would use callbacks or .then(), which can be harder to read.

Async functions always return a promise, even if you return a simple value.

Summary

Async and await make waiting for slow tasks easy and clean.

They help keep your program running smoothly without freezing.

Using them makes your code look like normal step-by-step code.

Practice

1. Why do we use async and await in JavaScript?

easy

A. To make the code run faster by skipping steps

B. To handle slow tasks without freezing the program

C. To write code that only works in old browsers

D. To stop the program completely until a task finishes

Solution

1. Step 1: Understand the problem with slow tasks

   Slow tasks like fetching data can freeze the program if handled synchronously.

2. Step 2: Role of async and await

   Async and await let the program wait for slow tasks without freezing, keeping it smooth.

3. Final Answer:

   To handle slow tasks without freezing the program -> Option B

4. Quick Check:

   Async/await = smooth waiting [OK]

Hint: Async/await = smooth waiting without freezing [OK]

Common Mistakes:

• Thinking async/await makes code faster
• Believing async/await stops the whole program
• Confusing async/await with old browser code

2. Which of the following is the correct way to declare an async function in JavaScript?

easy

A. function async fetchData() {}

B. function fetchData() async {}

C. async function fetchData() {}

D. function fetchData async() {}

Solution

1. Step 1: Recall async function syntax

   The correct syntax places async before the function keyword.

2. Step 2: Check each option

   Only async function fetchData() {} correctly uses async function fetchData() {}.

3. Final Answer:

   async function fetchData() {} -> Option C

4. Quick Check:

   Async before function keyword [OK]

Hint: Async keyword goes before function name [OK]

Common Mistakes:

• Placing async after function name
• Adding async inside function parentheses
• Writing async after function body

3. What will be the output of this code?

async function greet() {
  return 'Hello';
}

greet().then(console.log);

medium

A. 'Hello'

B. Promise { 'Hello' }

C. undefined

D. Error: greet is not a function

Solution

1. Step 1: Understand async function return

   An async function returns a Promise that resolves to the returned value.

2. Step 2: Using .then to get value

   The .then(console.log) prints the resolved value 'Hello'.

3. Final Answer:

   'Hello' -> Option A

4. Quick Check:

   Async function returns Promise, .then logs value [OK]

Hint: Async returns Promise; .then gets resolved value [OK]

Common Mistakes:

• Expecting direct string without .then
• Confusing Promise object with string
• Thinking async function returns undefined

4. Find the error in this code:

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

const result = fetchData();
console.log(result);

medium

A. data.json() is not a function

B. fetchData() should not be async

C. Cannot use await inside async function

D. Missing await before fetchData() call

Solution

1. Step 1: Check fetchData() call

   fetchData() returns a Promise, so logging it directly shows a Promise object.

2. Step 2: Fix by awaiting fetchData()

   Adding await before fetchData() inside an async context gets the resolved data.

3. Final Answer:

   Missing await before fetchData() call -> Option D

4. Quick Check:

   Await needed to get Promise result [OK]

Hint: Await async calls to get actual result [OK]

Common Mistakes:

• Logging Promise instead of awaited value
• Removing async keyword incorrectly
• Misunderstanding data.json() usage

5. You want to fetch user data and then fetch posts by that user. Which code correctly uses async/await to do this step-by-step without freezing the program?

function getUser() {
  return fetch('/user').then(res => res.json());
}

function getPosts(userId) {
  return fetch(`/posts?user=${userId}`).then(res => res.json());
}

// Fill in the blanks
async function loadData() {
  const user = _____ getUser();
  const posts = _____ getPosts(user.id);
  console.log(posts);
}

hard

A. await, await

B. await, then

C. then, await

D. then, then

Solution

1. Step 1: Understand async function usage

   Inside async functions, use await to wait for Promises step-by-step.

2. Step 2: Apply await to both calls

   Both getUser() and getPosts() return Promises, so both need await.

3. Final Answer:

   await, await -> Option A

4. Quick Check:

   Use await for sequential async calls [OK]

Hint: Use await for each async call inside async function [OK]

Common Mistakes:

• Mixing then and await inside async function
• Forgetting await causing Promise logs
• Using then without returning inside async