🚀 Web Development Interview Questions with Answers — Part 8: APIs & Backend Concepts

🧠 166. What is an API?

API stands for: 👉 Application Programming Interface

An API allows different software applications to communicate with each other.

Example:

When a weather app fetches weather data from a server, it uses an API.

Benefits:

✅ Data sharing

✅ System integration

✅ Automation

🧠 167. Difference Between REST and GraphQL

Concept | REST | GraphQL

Endpoints | Multiple endpoints | Single endpoint

Response structure | Fixed response structure | Client chooses data

Data fetching | Over-fetching possible | Fetch only needed data

Complexity | Simpler | More flexible

Example:

REST: GET /users/1

GraphQL:

{
  user(id:1){
    name
    email
  }
}

🧠 168. What is a RESTful API?

RESTful API follows REST architectural principles.

Key Principles:

Stateless

Client-Server Architecture

Uniform Interface

Resource-Based URLs

Example:

GET /users

POST /users

PUT /users/1

DELETE /users/1

🧠 169. What are HTTP Status Codes?

HTTP status codes indicate server response status.

Categories:

Range | Meaning

1xx | Informational

2xx | Success

3xx | Redirection

4xx | Client Error

5xx | Server Error

🧠 170. Explain 200, 201, 400, 401, 403, 404, and 500

Code | Meaning

200 | OK

201 | Created

400 | Bad Request

401 | Unauthorized

403 | Forbidden

404 | Not Found

500 | Internal Server Error

Example:

res.status(404).json({
   message: "User Not Found"
});

🧠 171. What is API Testing?

API Testing verifies functionality, performance, and security of APIs.

Checks:

✅ Response data

✅ Status codes

✅ Authentication

✅ Performance

Tools:

Postman

Insomnia

Swagger

🧠 172. What is Postman?

Postman is a tool used to test APIs.

Features:

✅ Send API requests

✅ Test endpoints

✅ Automate testing

✅ Manage collections

Example:

GET https://api.example.com/users

🧠 173. What is WebSocket?

WebSocket enables real-time two-way communication between client and server.

Uses:

Chat applications

Online gaming

Live notifications

Stock market updates

Benefits:

✅ Real-time communication

✅ Low latency

🧠 174. Difference Between Polling and WebSocket

Concept | Polling | WebSocket

Connection | Client repeatedly asks server | Persistent connection

Network usage | Higher network usage | Efficient communication

Updates | Slower updates | Real-time updates

🧠 175. What is Microservice Architecture?

Microservices divide an application into small independent services.

Example:

User Service

Payment Service

Order Service

Notification Service

Benefits:

✅ Scalability

✅ Independent deployment

✅ Easier maintenance

🧠 176. What is Monolithic Architecture?

Monolithic architecture combines all components into one application.

Example:

Frontend

Backend

Database

↓

Single Application

Advantages:

✅ Simpler development initially

Disadvantages:

❌ Harder to scale

🧠 177. What is Caching?

Caching stores frequently accessed data temporarily for faster retrieval.

Benefits:

✅ Faster performance

✅ Reduced database load

✅ Improved user experience

Example:

cache.set("users", data);

🧠 178. What is Redis?

Redis is an in-memory database commonly used for caching.

Features:

✅ Extremely fast

✅ Key-value storage

✅ Session management

Example:

redis.set("user", userData);