AJAX Tutorial

1. AJAX Introduction

What AJAX means, why it replaced full page reloads, and a simple conceptual example.

2. fetch() and XMLHttpRequest

XMLHttpRequest for context, then the modern fetch() API: GET/POST, headers, bodies, and async/await.

3. Working with JSON

Parsing and sending JSON with fetch, handling errors correctly, and a real-world example.

4. Error Handling and Retries

Timeouts with AbortController, idempotency, exponential backoff with jitter, and a complete retry wrapper.

5. AJAX Security: CSRF and CORS

The same-origin policy, CORS preflight requests explained concretely, CSRF attacks, and CSRF tokens.

6. Polling vs WebSockets vs SSE

A decision framework comparing short polling, long polling, Server-Sent Events, and WebSockets.

7. AJAX Interview Questions

Commonly asked AJAX and fetch() interview questions with clear, practical answers.