JavaScript is one of the most important programming languages today. Founded by Brendan Eich in 1995, it has done superbly well, not only in maintaining its status, but also in rising above all other programming languages.
The popularity of JavaScript is ever growing with no end in sight. Building web applications with JavaScript as the sole programming language has always been popular. And with this fast growing pace, the need for software engineers to have knowledge of JavaScript is only increasing. No matter what programming language you choose to excel at, JavaScript always crawls its way in to get involved with other programming languages as well, one way or the other.
There are a lot of technologies to choose from for the frontend and backend while developing an application. While this book uses Express.js for the backend, there are other frameworks as well, which you can learn if you want.
The other available backend frameworks are Meteor.js, Sails.js, Hapi.js, Mojito, Koa.js, and many others.
Similarly, for the frontend, the technologies include Vue.js, React, Angular, Backbone, and many more.
For databases, the options, other than MongoDB, are MySQL, PostgreSQL, Cassandra, and others.