Updated Ajax Interview Questions and Answers - 2025

Simple Ajax interview questions and answers for students and beginners. Includes short explanations, practical code samples (XMLHttpRequest, fetch, jQuery), and tips to answer confidently in interviews.

This guide is for students and beginner developers. Answers are short (under 5 lines), easy to read, and focused on what interviewers expect. You will also find small code samples and tips to prepare fast.

What is Ajax?

Ans: Ajax is abbreviated as Asynchronous Javascript and XML. It is new technique used to create better, faster and more interactive web systems or applications. Ajax uses asynchronous data transfer between the Browser and the web server. This technique is used to make internet faster and user friendly. It is not a programming language.

What are Ajax applications?

Ans: Browser based applications and platform independent applications are used by Ajax.

What are the advantages of Ajax?

Ans: Following are the advantages of Ajax:

• Bandwidth utilization
• It saves memory when the data is fetched from the same page.
• More interactive
• Speeder retrieval of data

What are the disadvantages of Ajax?

Ans: Following are the disadvantages of Ajax:

• AJAX is dependent on Javascript. If there is some Javascript problem with the browser or in the OS, Ajax will not support.
• Ajax can be problematic in Search engines as it uses Javascript for most of its parts.
• Source code written in AJAX is easily human readable. There will be some security issues in Ajax.
• Debugging is difficult (not impossible)
• Increases size of the requests
• Slow and unreliable network connection.
• Problem with browser back button when using AJAX enabled pages.

What are all the technologies used by Ajax?

Ans: AJAX uses following technologies:

• JavaScript
• XMLHttpRequest
• Document Object Model (DOM)
• Extensible HTML (XHTML)
• Cascading Style Sheets (CSS)

What Is the Format of an AJAX Request?

Ans: An AJAX request can be in any format:

• Text File
• HTML
• JSON object

How many types of triggers are present in update panel?

Ans: There are two types of triggers used in update panel:

1. PostBackTrigger : This works as full postback and it cannot work asynchronously
2. AsyncPostBackTrigger : Partial post back asynchronously

Is an AJAX Request Synchronous or Asynchronous?

Ans: AJAX requests are asynchronous by nature, which means that they should run in the background independently of other events.

What are the security issues with AJAX?

Ans: The Ajax calls are sent in plain text format, this might lead to insecure database access. The data gets stored on the clients browser, thus making the data available to anyone. It also allows monitoring browsing sessions by inserting scripts.

Is AJAX code cross browser compatible?

Ans: Not totally. Most browsers offer a native XMLHttpRequest JavaScript object, while another one (Internet Explorer) require you to get it as an ActiveX object

What are all the browsers support AJAX?

Ans: Following browsers support AJAX:

• Internet Explorer 5.0 and above
• Opera 7.6 and above
• Netscape 7.1 and above
• Safari 1.2 and above

How can you test the Ajax code?

Ans: JSUnit is the client side javascript code used as part of JUnit. JSUnit has been used for Ajax code.

How can you find out that an AJAX request has been completed?

Ans: ReadyState property is used to check whether AJAX request has been completed. If the property is equal to four, then the request has been completed and data is available.

What is JSON in Ajax?

Ans: JSON is abbreviated as JavaScript Object Notation. JSON is a safe and reliable data interchange format in JavaScript, which is easy to understand for both users and machines.

What are all the different data types that JSON supports?

Ans: JSON supports following data types:

• String
• Number
• Boolean
• Array
• Object
• Null

1) What does “asynchronous” mean in Ajax?

It means the request runs in the background. The page does not reload and the user can still click and type while data loads.

2) What is the difference between Ajax and a normal form submit?

Normal submit reloads the page and sends the whole form. Ajax sends only the needed data and updates a part of the page without reload.

3) What is JSON and why is it popular with Ajax?

JSON is a light data format that looks like JavaScript objects. It is easy to create, parse, and is smaller than XML in most cases.

4) What is the simplest way to do Ajax in modern JavaScript?

Use the fetch() API. It is built in, promise-based, and easy to read.

5) Show a tiny Ajax call using XMLHttpRequest. code

// GET text
const xhr = new XMLHttpRequest();
xhr.open('GET', '/hello.txt', true);
xhr.onload = () => console.log(xhr.responseText);
xhr.send();

6) Show a tiny Ajax call using fetch(). code

// GET JSON
fetch('/api/user')
  .then(r => r.json())
  .then(data => console.log(data))
  .catch(err => console.error(err));

7) Show a tiny Ajax call using jQuery. code

$.ajax({
  url: '/api/user',
  method: 'GET',
  dataType: 'json',
  success: d => console.log(d),
  error: () => console.log('error')
});

8) How do you send JSON with fetch (POST)?

fetch('/api/login', {
  method: 'POST',
  headers: {'Content-Type':'application/json'},
  body: JSON.stringify({email, password})
});

9) What is the Same-Origin Policy?

A page can request resources only from the same scheme, host, and port by default. This helps stop many attacks.

10) What is CORS?

Cross-Origin Resource Sharing. A server header-based rule that allows (or blocks) requests from other origins.

11) How do you handle Ajax errors quickly?

Catch errors and show a simple message. Also log details in the console or to your backend for debugging.

12) How can you cancel an in-flight Ajax request?

Use AbortController with fetch, or call xhr.abort() with XMLHttpRequest.

13) What is the difference between GET and POST in Ajax?

GET fetches data and adds params to the URL. POST sends data in the body and is better for creating or updating records.

14) Why use dataType: 'json' in jQuery Ajax?

It tells jQuery to parse the response as JSON automatically and give you a JS object in success callback.

15) How do you show a loader during an Ajax call?

Before the call, show a spinner element. On success/error, hide it and show the result message.

16) What is debouncing in Ajax search?

Wait a short time (like 300ms) after typing stops before sending the request. This reduces extra calls.

17) How do you parse JSON safely?

Use response.json() with fetch, or JSON.parse() inside a try/catch for raw strings.

18) Can Ajax calls be cached?

Yes. Browsers may cache GET responses. You can control with headers or add cache-busting query strings.

19) What is a typical REST flow with Ajax?

Use GET to read, POST to create, PUT/PATCH to update, and DELETE to remove. Return JSON responses.

20) How to send form data with Ajax?

Use FormData for files or use URLSearchParams/JSON for normal fields.

21) Show a small example: send form with fetch. code

const fd = new FormData(document.querySelector('#signup'));
fetch('/signup', { method:'POST', body: fd })
  .then(r => r.json()).then(d => console.log(d));

22) How do you handle JSON errors from server?

Check status code. If not 2xx, read JSON and show the message (e.g., validation failed). Always handle both paths.

23) What is CSRF and how does it relate to Ajax?

CSRF tricks a user into sending an unwanted request. For Ajax, send a CSRF token header or hidden field to protect.

24) Is Ajax only for JSON?

No. You can get text, HTML, XML, or binary files. JSON is just the most common for APIs.

25) How do you update only part of a page with Ajax?

Pick a target element (like #result) and set its innerHTML or textContent with the server response.

26) Can you chain Ajax calls?

Yes, with promises/async–await. Do one call, use its result to start the next call, etc.

27) What is a good HTTP status code for validation errors?

Use 400 (Bad Request) or 422 (Unprocessable Entity) with a JSON body describing the field errors.

28) How do you secure Ajax endpoints?

Require auth (cookie or token), validate inputs, rate limit if needed, and never trust client-only checks.

29) What is the role of headers in Ajax?

Headers carry extra info like content type, auth token, and CORS rules. Set them when needed.

30) Quick example: async/await with fetch. code

async function loadUser(){
  try{
    const r = await fetch('/api/user');
    if(!r.ok) throw new Error('Network');
    const data = await r.json();
    console.log(data);
  }catch(e){ console.error(e); }
}

Example A — GET JSON with fetch

fetch('/api/products')
  .then(res => res.json())
  .then(list => document.getElementById('out').textContent = JSON.stringify(list))
  .catch(() => alert('Failed to load'));

Example B — POST JSON with fetch

fetch('/api/contact', {
  method: 'POST',
  headers: {'Content-Type':'application/json'},
  body: JSON.stringify({name, email, message})
}).then(r => r.json())
  .then(d => console.log('Sent', d))
  .catch(() => console.log('Error'));

Example C — Debounced search

let t;
const box = document.getElementById('q');
box.addEventListener('input', () => {
  clearTimeout(t);
  t = setTimeout(() => {
    fetch('/api/search?q=' + encodeURIComponent(box.value))
      .then(r => r.json())
      .then(showResults);
  }, 300);
});

• Keep it short. Use 1–2 lines for the idea + 1 line for example.
• Think “user flow”. Say how Ajax keeps the page smooth (no full reload).
• Use simple code. Show fetch() or jQuery. Don’t over-explain.
• Mention security. Same-origin, CORS, CSRF token, validate on server.
• Be practical. Give a quick example: search-as-you-type or login form.
• Handle errors. Say “I check res.ok and show a message.”
• Use modern words. “Promise”, “async/await”, “JSON”.

1. Create a button that loads a joke from /api/joke and shows it in a div.
2. Build a search box with debounce (300ms) that calls /api/search?q=….
3. Send a small JSON object via POST and show the server’s reply message.
4. Try a request that fails (404) and show a friendly error on the page.

Ajax is not a language; it is a way to talk to the server without reloading the page. For interviews, remember three things: 1) Ajax improves user experience, 2) JSON is the common format, and 3) handle errors and security (CORS, CSRF, validation). If you can explain with one small example and a short code snippet, you will look confident and ready for a junior role.