What is a REST API?

🌐 Introduction to REST APIs

REST API stands for Representational State Transfer Application Programming Interface. Don't worry about the fancy name - it's simply a way for different software applications to communicate with each other over the internet.

Think of a REST API like a waiter in a restaurant:

• You (the client) - like a customer who wants to order food
• The API (the waiter) - takes your order and brings back your food
• The kitchen (the server) - prepares your order and sends it back

REST APIs are everywhere! When you:

• Check the weather on your phone app
• Post a photo on social media
• Order food through a delivery app
• Send a message in a chat app

Your app is likely talking to a REST API to get or send that information.

🔧 HTTP Methods (The API Verbs)

REST APIs use different HTTP methods (also called "verbs") to perform different actions. Think of these as commands you give to the API:

💻 Practical Examples with Our Fake API

Let's see these HTTP methods in action using our fake REST API. These examples work right now - you can copy and test them!

📖 GET: Reading Data

The most common operation - getting data from the API:

// Get all users
const users = await fetch('https://fake-rest-api-mobile-apps.vercel.app/api/users')
  .then(response => response.json());

console.log(users); // Array of user objects

// Get specific user by ID
const user = await fetch('https://fake-rest-api-mobile-apps.vercel.app/api/users/1')
  .then(response => response.json());

console.log(user); // Single user object

✍️ POST: Creating New Data

Adding new information to the API:

// Create a new user
const newUser = await fetch('https://fake-rest-api-mobile-apps.vercel.app/api/users', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({
    name: 'John Doe',
    email: 'john@example.com',
    phone: '+1-555-123-4567'
  })
}).then(response => response.json());

console.log(newUser); // The created user with new ID

🔄 PUT: Updating Data

Modifying existing information:

// Update user with ID 1
const updatedUser = await fetch('https://fake-rest-api-mobile-apps.vercel.app/api/users/1', {
  method: 'PUT',
  headers: {
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({
    name: 'Jane Smith',
    email: 'jane@example.com',
    phone: '+1-555-987-6543'
  })
}).then(response => response.json());

console.log(updatedUser); // The updated user data

🗑️ DELETE: Removing Data

Deleting information from the API:

// Delete user with ID 1
const response = await fetch('https://fake-rest-api-mobile-apps.vercel.app/api/users/1', {
  method: 'DELETE'
});

if (response.status === 204) {
  console.log('User deleted successfully!');
}

📊 HTTP Status Codes

When you make a request to an API, it responds with a status code that tells you what happened. Think of these like emoji reactions to your request:

📋 JSON: The Language of APIs

REST APIs typically send and receive data in JSON format (JavaScript Object Notation). JSON is like a universal language that all programming languages can understand.

JSON looks like this:

{
  "id": 1,
  "name": "John Doe",
  "email": "john@example.com",
  "isActive": true,
  "age": 30,
  "hobbies": ["reading", "coding", "gaming"],
  "address": {
    "street": "123 Main St",
    "city": "New York",
    "zipcode": "10001"
  }
}

JSON Rules:

• Strings must be in double quotes: "hello"
• Numbers can be integers or decimals: 42, 3.14
• Booleans are true or false: true, false
• Arrays use square brackets: [1, 2, 3]
• Objects use curly braces: {"key": "value"}

🎯 Understanding API Endpoints

An endpoint is like a specific address where you can find certain data. Each endpoint has a URL and accepts specific HTTP methods.

Endpoint Structure:

https://fake-rest-api-mobile-apps.vercel.app/api/users/123
         └─────────────────┘   └──────┘ └─────┘ └─┘
         Base URL             Path    Resource ID

Common Endpoint Patterns:

• /api/users - Get all users or create a new user
• /api/users/123 - Get, update, or delete user with ID 123
• /api/users/123/posts - Get all posts by user 123
• /api/posts?category=tech - Get posts filtered by category

🔍 Query Parameters

Query parameters let you filter, sort, and customize your API requests. They're added to the URL after a ? symbol.

Common Query Parameters:

// Pagination
/api/users?_page=2&_limit=10

// Filtering
/api/posts?userId=5&category=technology

// Searching
/api/users?q=john

// Sorting
/api/products?_sort=price&_order=asc

// Combining multiple parameters
/api/todos?userId=1&completed=false&_page=1&_limit=5

Try These with Our API:

// Get completed todos for user 50
const completedTodos = await fetch(
  'https://fake-rest-api-mobile-apps.vercel.app/api/todos?userId=50&completed=true'
).then(res => res.json());

// Get first 5 products
const products = await fetch(
  'https://fake-rest-api-mobile-apps.vercel.app/api/products?_page=1&_limit=5'
).then(res => res.json());

⭐ API Best Practices for Mobile Developers

1. Handle Errors Gracefully

async function fetchUserSafely(userId) {
  try {
    const response = await fetch(`/api/users/${userId}`);
    
    if (!response.ok) {
      throw new Error(`HTTP ${response.status}: ${response.statusText}`);
    }
    
    const user = await response.json();
    return user;
  } catch (error) {
    console.error('Failed to fetch user:', error.message);
    // Show user-friendly error message
    return null;
  }
}

2. Use Loading States

const [users, setUsers] = useState([]);
const [loading, setLoading] = useState(true);
const [error, setError] = useState(null);

useEffect(() => {
  fetchUsers()
    .then(data => {
      setUsers(data);
      setLoading(false);
    })
    .catch(err => {
      setError(err.message);
      setLoading(false);
    });
}, []);

3. Respect Rate Limits

• Don't make too many requests too quickly
• Check rate limit headers in responses
• Implement retry logic with exponential backoff
• Cache responses when possible

4. Validate Data

• Always validate data before sending to API
• Check required fields are present
• Validate data types and formats
• Show clear validation error messages

🧪 How to Test APIs

There are several ways to test REST APIs. Here are the most popular tools:

1. Browser Developer Tools

Press F12 in your browser and use the Network tab to see API requests in real-time.

2. Postman

A popular desktop app for testing APIs with a user-friendly interface.

3. curl (Command Line)

# GET request
curl https://fake-rest-api-mobile-apps.vercel.app/api/users

# POST request
curl -X POST \
  -H "Content-Type: application/json" \
  -d '{"name":"John","email":"john@example.com"}' \
  https://fake-rest-api-mobile-apps.vercel.app/api/users

4. Our Interactive Tester

We have a built-in API tester on our main page! You can test all endpoints without writing any code.

🚀 Next Steps

Now that you understand REST APIs, here's what you can do next:

1. Practice with our API: Use our interactive tester to try different endpoints
2. Build a simple app: Create a mobile app that displays data from our API
3. Learn about authentication: Most real APIs require API keys or OAuth
4. Explore advanced topics: Pagination, webhooks, rate limiting
5. Read API documentation: Practice reading real API docs from services you use