How to get user.id from jwt token in Node.js? | what is jwt token and how it works

how To get the user ID from a JWT token in a Node.js application, you need to first decode the token and then extract the user ID from it. Here's an example code snippet to do so:

const jwt = require('jsonwebtoken');

// Assuming the JWT token is stored in a variable called "token"

const decodedToken = jwt.decode(token);

// Assuming the user ID is stored in the "id" field of the JWT token

const userId = decodedToken.id;

console.log('User ID:', userId);

In the above code, we first require the jsonwebtoken module, which is used to decode and verify JWT tokens. We then call the jwt.decode function with the JWT token, which returns the decoded token as a JavaScript object.

Assuming that the user ID is stored in a field called id in the JWT token, we can extract it from the decoded token object and store it in a variable called userId. Finally, we log the user ID to the console.

Note that this code only decodes the JWT token and extracts the user ID from it. If you also need to verify that the token is valid and has not been tampered with, you will need to use the jwt.verify function instead of jwt.decode.

what is jwt token and how it works (JSON Web Token)

JWT (JSON Web Token) is a type of token used for authentication and authorization in web applications. It is a compact, self-contained data structure that is used to securely transmit information between parties as a JSON object.

In Node.js, you can use third-party libraries such as jsonwebtoken to generate and verify JWT tokens. Here's a brief overview of how it works:

1. The client sends a request to the server with their login credentials.
2. The server verifies the credentials and generates a JWT token using the jsonwebtoken library.
3. The server sends the JWT token back to the client in the response.
4. The client stores the JWT token in local storage or a cookie.
5. For subsequent requests, the client includes the JWT token in the request headers.
6. The server verifies the JWT token using the jsonwebtoken library, and if it is valid, grants access to the requested resource.

Here's an example of how to generate a JWT token in Node.js using the jsonwebtoken library:

const jwt = require('jsonwebtoken');

const payload = {

  user_id: 123,

  username: 'john_doe',

  role: 'admin'

};

const secretKey = 'my_secret_key';

const token = jwt.sign(payload, secretKey, { expiresIn: '1h' });

In this example, we're creating a JWT token with a payload containing the user ID, username, and role. We're also specifying a secret key that will be used to sign the token, and an expiration time of 1 hour.
To verify a JWT token, you can use the jsonwebtoken library like this:

const token = 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...';

const secretKey = 'my_secret_key';

jwt.verify(token, secretKey, (err, decoded) => {

  if (err) {

    // Handle invalid token

  } else {

    // Token is valid, get the user information from the decoded payload

    const { user_id, username, role } = decoded;

  }

});