Tell me about HTTP request methods and their main differences (GET, POST, PUT, DELETE, PATCH, HEAD).

HTTP methods define the action that the client wants to perform on a resource on the server:

• GET — requests data from the server. A safe and idempotent method, it should not change the server's state.
• POST — sends data to the server to create a new resource or perform an operation. Not idempotent.
• PUT — completely replaces an existing resource or creates it if it does not exist. Idempotent.
• DELETE — deletes the specified resource. Idempotent.
• PATCH — partially updates a resource by sending only the changed fields. Not always idempotent.
• HEAD — requests only the response headers, without the body. Used to check the existence of a resource or metadata.

Example usage in fetch (JavaScript):

// GET request
fetch('/api/items')
  .then(res => res.json())
  .then(data => console.log(data));

// POST request
fetch('/api/items', {
  method: 'POST',
  headers: {'Content-Type': 'application/json'},
  body: JSON.stringify({name: 'New Item'})
});