Decode Jwt Token in Node - without Library

Question

I have a following code to decode the Jwt token in Javascript (ref: How to decode jwt token in javascript)

const token = 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c';

function parseJwt(token) {
  var base64Url = token.split('.')[1];
  var base64 = base64Url.replace(/-/g, '+').replace(/_/g, '/');
  console.log(JSON.parse((atob(base64))))
};

parseJwt(token);

I am getting the payload which I needed from above code But I am implementing it in node where we dont have "atob" function to decode the base64 encoded string

Seems we need to use Buffer in node. Did my research and came up with below solution which didn't work.

const token = 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c';
function parseJwt(token) {
  const base64Url = token.split('.')[1];
  const base64 = base64Url.replace(/-/g, '+').replace(/_/g, '/');
  const buff = new Buffer(base64, 'base64');
  const payloadinit = buff.toString('ascii');
  const payload = JSON.parse(payloadinit);
  console.log(payload)
};
parseJwt(token);

Please let me know if there is any better approach - No libraries(Jwt, or decode-Jwt)

score 8 · Accepted Answer · answered Oct 17 '18 at 21:04

8

Actually I have tried it in independent environment and above code works like charm for getting Jwt token pay load

const token = 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c'

const base64Url = token.split('.')[1];
const base64 = base64Url.replace(/-/g, '+').replace(/_/g, '/');
const buff = new Buffer(base64, 'base64');
const payloadinit = buff.toString('ascii');
const payload = JSON.parse(payloadinit);
console.log(payload);

https://repl.it/@Punith/RuralSeveralAdaware

answered Oct 17 '18 at 21:04

Mahesh

221
1
3
14

Thanks! in node 10 and above, use `const buff = Buffer.from(base64, "base64");` instead of new Buffer. – david Nov 06 '21 at 07:53
In node >= 14.18, directly use `Buffer.from(base64Url, 'base64url')` instead of doing `replace`s. – Pascal Pixel Rigaux Apr 14 '22 at 11:58

score 2 · Answer 2 · answered Nov 21 '19 at 17:27

2

const DecodeJWT= (token) => {
  try {
    return JSON.parse(atob(token.split('.')[1]));
  } catch (e) {
    return null;
  }
};

simple & easy way

answered Nov 21 '19 at 17:27

Kashan Haider

1,036
1
13
23

great solution, also doable directly in client without requiring a Buffer – Rich Steinmetz Dec 23 '19 at 11:54

Decode Jwt Token in Node - without Library

2 Answers2

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