Glimmer is a fairly new library and was built in 2017 by the creative minds behind Ember.js. It was designed for “fast and light-weight UI components for the web.” It was created to serve as a lighter and smaller Ember.js and can also be used with Ember.js as a component as well as run standalone. In order to make it run faster, Glimmer compiles your templates into low level code without sacrificing the ease of use.
Underscore, first created in 2009, is a utility library which is primarily useful for manipulating arrays, objects and other functions.It has over 100 different functions for that effect. One of the most powerful features of Underscore is its functional programming helpers.Functional programminghas become increasingly popular in the last few years as it is a programming paradigm that avoids changing state and mutating data, which can be quite useful. The most popular Underscore functions are map, filter and reduce.