Nowadays Javascript is the most popular and widely used programming language, so the ecosystem around it constantly grows.
However, it is expected that the small "standard library" of Javascript will remain so. To fill this gap, many of the most popular utility libraries have grown on GitHub. Here is a short list of useful and highly maintained libraries.
1. MathJS
Math.js is an extensive mathematical library for JavaScript and Node.js, compatible with the Math library integrated in JavaScript. The library contains a flexible parser for expressions, is capable to perform symbolic calculations, and has a large set of functions and integrated constants. You can also extend it yourself.
2. Moment/date-fns
Momentjs is easy to use, support various functions to operation of Date. It is defined object type and use like new Date(). For your convenience, it support unordered function parameter although it was deprecated now. momentjs was made to handle Date/Time and the set of these concept. For this reason, It can be a OOP library.
Date-fns is a time manipulation library for Javascript, chosen by many developers to replace moment.js providing over 130 functions to manipulate dates in the browser and in Node.js. Date-fns is built using pure functions and keeps things unaltered without changing the instances of past dates. It works well with bundlers like webpack, Browserify, or Rollup and also supports tree-shaking.
One of the biggest difference is that date-fns is immutable but momentjs is mutable. date-fns return new Date instance from function which was run. But momentjs change its own state.
3. Sugar
Sugar is a Javascript utility library for working with native objects. Custom constructions and modular npm packages allow you to use only what you need and users can define methods or use plugins to handle specialized use cases.
4. CollectJS
Collect.js is a free wrapper for working with arrays and objects in Javascript with dozens of useful features and APIs that is (almost) identical to Laravel Collections5.5. The library is actively maintained, and it's worth keeping an eye on.
5. ChartJS
Chart.js is has 8 different types of data display, each of which animated and customizable. Chart.js allows you to create simple HTML5 charts using the tag, with great rendering performance on all modern browsers. Definitely one of the most useful and elegant libraries in the list.
6. Mout
Mout.js is a collection of modular JavaScript utilities that can be used in the browser as AMD modules or on node.js. Mout provides helper methods similar to those found on other languages standart libraries (Python, Ruby, PHP etc) and lets you load only the modules/functions you need, and provides a consistent API and normalizes behavior across multiple browsers.