Well there is no straight answer to this questions but let’s see if we can help you answer it.
Case I: Javascript is the only programming language you know
Let’s say Javascript is the one programming language you know and you are working as a front-end developer with HTML, CSS & Js. In that case, it is recommended that you level up your game and move to ReactJS and level up your game.
To be honest, if you are working on small projects you really don’t need to learn ReactJs however if you want to work with tech giants such as Amazon, Facebook & Others, ReactJs is something which one can’t do away with while making these websites. Top websites using ReactJs
One advantage of learning ReactJs is that you can start with ReactNative (though they are different but concepts are similar) & move to mobile application development as well.
Case II: Along with JS you know bit of PHP
In this case, you can either move towards learning PHP Frameworks such as CodeIgnitor (to start with) & later move to Laravel. There are a number of small and mid level companies who use Laravel for their development needs. 1.1 Million Websites are using Laravel
Case III: Along with JS you know basics of Python
If you enjoy working with Python, you can consider focusing on it completely as the language is known as a versatile language. Python can be used for Data Mining, Data Science, AI & Machine Learning too. Why learn python will give you good insights.
Conclusion
It totally depends on where you are and what you want to be, let’s say if you are more inclided towards moving to backend programming, then you may skip ReactJs however, if front end excites you & you are totally into JavaScript, ReactJs in today’s time seems to be a legit option.
PS: ReactJs has some high paying jobs too, however we skipped that part since we want your decision to be based on your interest & not based on the monetary benefits.