In this article, I would like to suggest a few best Javascript utility libraries that are useful and highly maintained libraries. The source code of these JavaScript libraries hosted and maintained on GitHub.

1. Underscore - https://underscorejs.org/

Underscore is a JavaScript library that provides a whole mess of useful functional programming helpers without extending any built-in objects. It’s the answer to the question: “If I sit down in front of a blank HTML page, and want to start being productive immediately, what do I need?” … and the tie to go along with jQuery's tux and Backbone's suspenders.

GitHub Link - https://github.com/jashkenas/underscore
For Docs, License, Tests, and pre-packed downloads: http://underscorejs.org
Website - https://underscorejs.org/

2. Lodash - https://lodash.com/

A modern JavaScript utility library delivering modularity, performance & extras. Lodash, NPM’s most downloaded and most dependent-upon package, was built to provide more consistent cross-environment iteration support for arrays, strings, objects, and arguments objects.

GitHub link - https://github.com/lodash/lodash
For Docs - https://lodash.com/docs/4.17.11
Website - https://lodash.com/

3. MathJs - https://mathjs.org/

Math.js is an extensive math library for JavaScript and Node.js. It features a flexible expression parser with support for symbolic computation, comes with a large set of built-in functions and constants, and offers an integrated solution to work with different data types like numbers, big numbers, complex numbers, fractions, units, and matrices. Powerful and easy to use.

GitHub Link - https://github.com/josdejong/mathjs
For Docs - https://mathjs.org/docs/index.html
Examples - https://mathjs.org/examples/index.html
Website - https://mathjs.org/

4. Moment - http://momentjs.com/

A lightweight JavaScript date library for parsing, validating, manipulating, and formatting dates.

GitHub Link - https://github.com/moment/moment/
Documentation - http://momentjs.com/docs/
Website - http://momentjs.com/

5. Sugar - https://sugarjs.com/

Sugar is a Javascript utility library for working with native objects.

GitHub link - https://github.com/andrewplummer/Sugar
Documentation - https://github.com/andrewplummer/Sugar#documentation
Website - https://sugarjs.com/

6. Lazy - http://danieltao.com/lazy.js/

Lazy.js is a functional utility library for JavaScript, similar to Underscore and Lodash, but with a lazy engine under the hood that strives to do as little work as possible while being as flexible as possible.