JavaScript is the most popular programming language in Web, way ahead of popular ones like Perl, Ruby, and Python. It is also one of the essential skills for any Web developer. It is even true for Java developers. If you have JavaScript in your resume or LinkedIn profile, you will likely receive many Job opportunities. Everybody wants polyglots, programmers who know multiple programming languages because most of the real-world projects are developed with multiple technologies, you will always found some component is written in Java, some in C++, then you have JSP, Server, jQuery, JavaScript, etc. for web pages and so on. In short, it's essential to learn JavaScript in today's competitive world.