NumVerify offers a full-featured yet simple RESTful JSON API for national and international phone number validation and information lookup for a total of 232 countries around the world.

Day.js is a minimalist JavaScript library that parses, validates, manipulates, and displays dates and times for modern browsers with a largely Moment.js-compatible API. If you use Moment.js, you already know how to use Day.js.

A declarative, efficient, and flexible JavaScript validation library for Humans. V4f provides a lot of rules that you can use to build complex validation without the need to be a javascript expert.

Learn how to compare two dates in JavaScript with various methods by Saruque Ahamed Mollick.