1. What is an API?

• API (Application Programming Interface) = a way for applications to communicate.
• In web apps → API acts like a messenger between frontend (browser/mobile app) and backend (server + database).
• Instead of HTML pages, APIs usually return JSON data.

📌 Example:

GET /api/users/123
Response:
{ "id": 123, "name": "Alice", "email": "[email protected]" }

2. REST API Basics

REST (Representational State Transfer) is the most common API style.

• Uses HTTP methods to interact with resources:
  • GET → Fetch data
  • POST → Create data
  • PUT → Update/replace data
  • PATCH → Modify part of data
  • DELETE → Remove data
• Returns JSON or XML.
• Each resource has a URL endpoint.

📌 Example:

GET /api/products       → Get all products
GET /api/products/10    → Get product with ID 10
POST /api/products      → Add a new product
PUT /api/products/10    → Update product 10
DELETE /api/products/10 → Delete product 10

3. GraphQL Basics

• GraphQL = newer API query language (by Facebook).
• Instead of multiple endpoints, you have one endpoint (usually /graphql).
• Client specifies exact data it wants → prevents over-fetching/under-fetching.