JavaScript has clearly become one of the most popular languages in the 21st century ever since the introduction of the server-side JavaScript NodeJs. A lot of frontend frameworks have popped up which means you can become a full-stack developer with one language and of course, you need a bit of HTML5 and CSS3 skills to sexy up your frontend.
Being a JavaScript developer doesn’t mean you are just a web developer you can also become a cross-platform mobile web application developer with the help of frameworks like react-native , ionic to mention but a few. You can also do some machine learning and implement some machine learning models using TensorFlow.js this means your web applications will be smarter using just JavaScript.
Game development is also now possible with JavaScript using frameworks like p5.js there are some YouTube Videos with examples for this.
The JavaScript ecosystem and community has become one of the biggest programming communities on the internet. This is because of its popularity and the node package manager (npm). The package manager accesses over a million repositories of open source code packages that mostly simplify your development process. If you want to manipulate time and dates there is momentjs, if you want to hash your passwords and secrets for security and authentication there bcryptjs, if you want a series of utility functions to help manipulate strings, arrays, objects and many more there is lodash. Long story short with npm there is no need to rewrite code if common fixes there is a high probability that there is a npm package that does exactly the same so you just have to utilize it.
In conclusion, JavaScript is a language just like any other mainstream language out there it is no longer bound to the browser like the old days so I would recommend it as a starting point if you are new to development and programming. To get started take the JavaScript Algorithms and Data Structures course from FreeCodeCamp. If you haven’t written any JavaScript and you are now a good developer with some other language I recommend you get started with a few javascript.
These three are popular JavaScript front frameworks to look into and I have personally tried them