Moment.js is an invaluable tool for developers who need to work with date and time. It's a lightweight JavaScript library that makes it easy to parse, validate, manipulate, and display dates and times in both the browser and Node.js. Moment.js provides a simple API, allowing developers to quickly and easily access date and time related functionality. With Moment.js, developers can easily add, subtract, and compare dates, as well as format and display dates in various formats. Moment.js is also completely customizable, allowing developers to modify the library to fit their exact needs. This powerful library is a must-have for any developer working with dates and times!