What is an API?

API stands for Application Programming Interface. It’s a set of rules for how programs can talk to each other. When building web applications, APIs define how frontends can request data from backends.

You’ve already used APIs as a frontend developer with the provided Noroff APIs.

REST APIs

REST (Representational State Transfer) is a popular way to structure APIs. Most web APIs you’ll encounter use REST.

What makes an API “RESTful”?

  1. Uses standard HTTP methods:

    • GET: Retrieve data
    • POST: Create new data
    • PUT: Update existing data (replace entirely)
    • PATCH: Update existing data (partial update)
    • DELETE: Remove data

  2. URLs represent resources (things in your system):

    /users          - represents all users
/users/123      - represents the user with ID 123
/users/123/posts - represents all posts by user 123

  3. Returns data in a consistent format (usually JSON):

    {
  "id": 123,
  "name": "Sarah Chen",
  "email": "sarah@example.com"
}

  4. Stateless - each request stands alone. The server doesn’t remember anything between requests. Each request must contain all the information needed to understand and process it.

Practical REST Examples:

GET    /products         - Get all products
GET    /products/456     - Get product with ID 456
POST   /products         - Create a new product
PUT    /products/456     - Update product 456
DELETE /products/456     - Delete product 456
  • Works with standard HTTP (no special protocols)
  • Simple to understand and implement
  • Supported by all programming languages
  • Easy to test with browser tools

Other API Patterns

While REST is the most common, you might encounter other API patterns:

  • GraphQL: Lets clients request exactly what data they need in a single request
  • SOAP: Older XML-based protocol, more complex and less common now
  • WebSockets: For real-time, two-way communication (chat apps, live score updates)

We’ll focus on REST as it’s the most common and straightforward for building APIs.

Tags: