When writing pre-request scripts and test scripts as part of a Postman request, you aren't limited to vanilla JavaScript. There are a handful of libraries that can be required where needed.
This short list of available libraries includes cherrio, lodash, and
moment.
To pull one of these into a particular script, use the standard require
feature:
var moment = require('moment');
var now = moment();For a full list of what is available, check out Postman's Sandbox API Reference.