Synchronous vs Asynchronous

Synchronous

var jwt = require('jsonwebtoken');
var token = jwt.sign({ foo: 'bar' }, 'shhhhh');

Asynchronous

var token = jwt.sign({ foo: 'bar' }, 'shhhhh', function(err, token) {
  console.log(token);
);

I want to know , is it bad to use Synchronous way , in express js server? is there any benefit with Asynchronous mode? As I think there is no I/O and just CPU usage, So Asynchronous and Synchronous must b same, just syntax is different

[ziluvatar]

TL;DR; To allow consumers load keys from filesystem or any other source of ReadStream without blocking event loop. Not to actually perform the signing.

I’ve been digging into git history and jws implementation to understand why the library provided the async functionality for signing:

• Back in 2013, jws implemented streaming for sign/verify: https://github.com/brianloveswords/node-jws/commit/ad80a8ac9fdea2de59b607ea8f556451053af145
• In 2015 that was used by this library https://github.com/auth0/node-jsonwebtoken/pull/127 , however, in my opinion, they misunderstood “streaming support” with “async signing”.
• jws library provides streaming for payload and secret, that way you could load those from the file system or any source that provided a NodeJS stream interface, like we can see in jws: https://github.com/brianloveswords/node-jws/blob/ad80a8ac9fdea2de59b607ea8f556451053af145/test/jws.test.js#L132
• On this library we supported both streams until v7.4.3 -> v8.0.0 where we lost compatibility with stream payload ( not known breaking change 🎉 😞, I just updated the migration notes v7 -> v8 ).

Honestly, not sure if that streaming is a desired feature by consumers, we’d need to update the README to make it clear.

[lonix1]

If there is no perf difference, why does the library offer an async alternative?