HTTP & APIs
API
An API is a defined contract that lets one software component request data or actions from another without knowing its internal implementation.
Diagram
Mobile App ──▶ [API Contract] ──▶ Backend Server
(endpoints + rules) (hidden internals)
Client only sees: GET /users, POST /orders
Client never sees: database schema, business logicIn Depth
API stands for Application Programming Interface. A web API exposes a set of endpoints and rules that external clients (mobile apps, other services, third-party developers) use to read or modify data.
Code Example
Calling a public API
const response = await fetch('https://api.stripe.com/v1/charges', {
method: 'POST',
headers: { 'Authorization': 'Bearer sk_live_...' },
body: JSON.stringify({ amount: 2000, currency: 'usd' }),
});
const charge = await response.json(); // 201 Created⚠️ Common Misconception
An API is not the same as a database. The API is the controlled front door; the database is the private storage room behind it. Clients should never connect to the database directly.
🌍 Real World Usage
Stripe's payment API, GitHub's repo API, and Twitter's timeline API power thousands of third-party apps — all through HTTP endpoints.