One thing is certain - JavaScript is eating the world. Every website - big or small, is using JavaScript. It was and still is the language of the Web. And because HTML5 as a standard is evolving with supersonic speed, more and more companies are embracing it. Take for example the gaming industry. Companies like Riot, NCSoft, Blizzard, EA, to name a few, are using HTML5 (HTML, CSS and JavaScript) for their game UIs. The reason - JavaScript is great for UI interaction and presentation. It's powerful enough to meet the needs of almost all companies and industries.
But JavaScript is not the almighty, use-for-everything and everywhere language. Like most of the people will tell you - use the right tools for the right job. Are you going for low level programming? Well, JavaScript in not even near to languages like C or C++. Looking for performance wise mobile application, where millions of users will interact with different parts of the app simultaneously? Swift/Object-C and Java would probably be a better choice than NativeScript, Ionic or Cordova.
Although I wouldn't use the word "must", I would still advice you to learn JavaScript, even if you are not going to use if extensively. Sooner or later you will encounter a piece of code written in JavaScript. That is inevitable. But don't stop there. Learn Ruby and understand how it handles Object Oriented Programming. Learn Haskell and see why more and more developers are embracing the functional programming paradigms. Try C++ or Rust to see the power and performance they have.
The more languages you know, the broader perspectives you will have about solving different problems.