getgroups

The process.getgroups() method returns an array with the supplementary group IDs. POSIX leaves it unspecified if the effective group ID is included but Node.js ensures it always is.

import process from 'node:process';

if (process.getgroups) {
  console.log(process.getgroups()); // [ 16, 21, 297 ]
}

This function is only available on POSIX platforms (i.e. not Windows or Android).