GET and POST are the two most commonly used HTTP request methods. They differ significantly in data transmission, security, and use cases. Below is a detailed comparison.

I. Similarities

1. Based on HTTP Protocol: Both are used for data exchange between client and server.
2. Can Transmit Data: Although methods differ, both can send data (GET via URL query parameters, POST via request body).
3. Idempotency: Strictly speaking, GET is idempotent (multiple identical requests produce the same result), while POST is non-idempotent (multiple submissions may cause side effects). However, in practice, developers must ensure this behavior.

II. Core Differences

III. Use Cases

1. GET Use Cases

• Fetching Data: Retrieving information (e.g., search, pagination, filtering).

GET /users?id=123

• Idempotent Operations: Refreshing pages, fetching static resources (images, CSS).
• Sharable Links: Parameters visible in URL, easily copied and shared (e.g., product detail pages).

2. POST Use Cases

• Submitting Sensitive Data: Login forms, payment information.

POST /login
Content-Type: application/json

{
    "username": "admin",
    "password": "123456"
}

• Large Data Transmission: File uploads, submitting long text (e.g., blog content).
• Non-idempotent Operations: Creating orders, deleting resources, updating data (e.g., user profile updates).

IV. Important Considerations

1. Security:

   • Even with POST, sensitive data should be transmitted over HTTPS.
   • Avoid passing passwords or tokens via GET.

2. RESTful API Design:

   • GET corresponds to Read (retrieve). POST corresponds to Create.
   • Other methods: PUT (update), DELETE (remove), etc.

3. Practical Limits:

   • The "no length limit" for POST is theoretical. Servers (e.g., Nginx) may configure client_max_body_size to restrict request body size.

4. Browser Beahvior:

   • When refreshing a POST request, browsers may prompt to confirm resubmission (due to potential side effects).

V. Code Examples

GET Request (Frontend)

// Passing parameters via URL
fetch('/api/search?keyword=apple')
  .then(response => response.json());

POST Request (Frontend)

// Parameters in request body
fetch('/api/login', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ username: 'admin', password: '123' })
});

Backend Handling (Node.js with Express)

// GET parameters parsed from URL
app.get('/api/search', (req, res) => {
  const keyword = req.query.keyword; // Gets ?keyword=apple
  // ... process and respond
});

// POST parameters parsed from request body
app.post('/api/login', (req, res) => {
  const { username, password } = req.body; // Gets JSON data
  // ... authenticate and respond
});

Summary

• Use GET: For simple, non-sensitive data that benefits from caching or link sharing.
• Use POST: For sensitive, large, or state-changing operations.
• Key Principle: Follow RESTful conventions and choose the method based on the operation's semantics.