• Ecmascript 6
• Frameworks (React, Ember, Angular are the big three)
Beyond that, it's important to understand the pain points that people are trying to solve. For instance, why is React a better approach to front-end UI's than MVC? Is JSX a reasonable approach to the DOM, and is it worth breaking conventional wisdom? What problem does Facebook's css-layout solve? What issues with modularity and reusability are people trying to solve, and how is this different at different scales of complexity? What's the "why" behind the changes to ES6?
And even beyond that, look at the future, and see what people are trying to solve that nobody has quite solved yet.
In other words, don't just understand what you can do with Javascript, understand what hurts and how people are trying to fix it, or at least make it hurt less.