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Master the Basics of APIs

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Master the Basics of APIs

Master the Basics of APIs

1. HTTP Protocol

  • HTTP Methods: HTTP defines a set of request methods for interacting with resources. The most commonly used methods are:
    • GET: Retrieve data from a server (read).
    • POST: Send data to the server to create a new resource (create).
    • PUT: Update an existing resource (update).
    • DELETE: Remove a resource (delete).
  • HTTP Headers: Headers provide additional information about the request or response, such as content type (Content-Type: application/json) or authentication information.
  • Status Codes: HTTP responses come with status codes to indicate the outcome of the request:
    • 200: OK (success).
    • 201: Created (resource successfully created).
    • 400: Bad Request (client-side error).
    • 404: Not Found (resource not found).
    • 500: Internal Server Error (server-side issue).

Example:

javascript
const express = require('express');
const app = express();app.use(express.json());

let users = [];

// GET request to fetch users
app.get(‘/users’, (req, res) => {
res.status(200).json(users); // 200 OK
});

// POST request to create a new user
app.post(‘/users’, (req, res) => {
const newUser = req.body;
users.push(newUser);
res.status(201).json(newUser); // 201 Created
});

// Error handling for unknown routes
app.use((req, res) => {
res.status(404).json({ message: “Resource not found” }); // 404 Not Found
});

app.listen(3000, () => console.log(‘Server running on port 3000’));

2. RESTful Principles

REST (Representational State Transfer) is an architectural style used to design web services. It relies on:

  • Statelessness: Each request from the client to the server must contain all necessary information, as the server does not store client context.
  • URIs (Uniform Resource Identifiers): Resources are accessed through URIs like /users, /products.
  • HATEOAS (Hypermedia As The Engine Of Application State): A RESTful system provides hypermedia links to let clients discover actions dynamically.

Example:

javascript
// Express routes implementing RESTful structure
app.get('/users', (req, res) => { /* Get all users */ });
app.post('/users', (req, res) => { /* Create a new user */ });
app.put('/users/:id', (req, res) => { /* Update user by ID */ });
app.delete('/users/:id', (req, res) => { /* Delete user by ID */ });

In REST, you map HTTP methods to CRUD operations:

  • GET /users -> Fetch all users.
  • POST /users -> Create a new user.
  • PUT /users/:id -> Update a user by ID.
  • DELETE /users/:id -> Delete a user by ID.

3. JSON/XML

  • JSON (JavaScript Object Notation) is the most commonly used data format for APIs today due to its simplicity and ease of use. It’s used to represent structured data.
  • XML (eXtensible Markup Language) is another format, though less commonly used today, mostly in legacy systems.

Example (Handling JSON in Express):

javascript
// Middleware to parse incoming JSON requests
app.use(express.json());app.post(‘/data’, (req, res) => {
const jsonData = req.body;
res.status(200).json({
message: “Received data”,
data: jsonData
});
});

This example receives JSON data from the client and returns it in the response.

4. CRUD Operations

CRUD refers to the four basic operations that can be performed on data:

  • Create: Add new records (e.g., POST).
  • Read: Retrieve data (e.g., GET).
  • Update: Modify existing data (e.g., PUT or PATCH).
  • Delete: Remove records (e.g., DELETE).

Complete Example (CRUD Operations using Node.js and Express):

javascript
const express = require('express');
const app = express();app.use(express.json());

let users = [
{ id: 1, name: ‘John Doe’, age: 25 },
{ id: 2, name: ‘Jane Doe’, age: 28 }
];

// CREATE: Add a new user (POST)
app.post(‘/users’, (req, res) => {
const newUser = {
id: users.length + 1,
name: req.body.name,
age: req.body.age
};
users.push(newUser);
res.status(201).json(newUser); // 201 Created
});

// READ: Get all users (GET)
app.get(‘/users’, (req, res) => {
res.status(200).json(users); // 200 OK
});

// UPDATE: Update an existing user (PUT)
app.put(‘/users/:id’, (req, res) => {
const userId = parseInt(req.params.id);
const user = users.find(u => u.id === userId);
if (!user) {
return res.status(404).json({ message: ‘User not found’ }); // 404 Not Found
}
user.name = req.body.name;
user.age = req.body.age;
res.status(200).json(user); // 200 OK
});

// DELETE: Remove a user (DELETE)
app.delete(‘/users/:id’, (req, res) => {
const userId = parseInt(req.params.id);
const userIndex = users.findIndex(u => u.id === userId);
if (userIndex === –1) {
return res.status(404).json({ message: ‘User not found’ }); // 404 Not Found
}
users.splice(userIndex, 1);
res.status(204).end(); // 204 No Content
});

app.listen(3000, () => console.log(‘Server running on port 3000’));

Key Highlights in Example:

  • POST (/users): Adds a new user and responds with the created user and status code 201 Created.
  • GET (/users): Retrieves all users and returns them with status code 200 OK.
  • PUT (/users/:id): Updates a user by ID. If the user does not exist, it returns 404 Not Found.
  • DELETE (/users/:id): Deletes a user by ID and returns status code 204 No Content upon successful deletion.

Conclusion

This covers the essentials of:

  • HTTP Protocol: Understanding methods, headers, and status codes.
  • RESTful Principles: Designing stateless APIs with a proper URI structure.
  • JSON/XML: Handling data exchange formats.

CRUD Operations: Implementing basic database actions via HTTP methods in Express.

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