My current job is mostly Perl most of the time but that often means understanding and working with transport layers and standards not directly related to Perl and a lot of front end development. The work is 85% JavaScript right now to complete a big front-end project. I am forced to do Java and PHP rarely for work.
If you are interested in modern JavaScript (ECMAScript 6), the work pool is lagging behind the technology and the death throes of Flash (ActionScript) and the acceleration of browsers picking up new standards mean that an ES6 oriented JS dev will be in demand. I’m trying to play catch-up there right now. JS still has some irritating wrinkles but it’s a more fun, useful, and interesting language than it used to be and it has a burgeoning ecosphere.