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Whether you like it or not, if you’re going to be a web developer(front-end especially) you have to know Javascript. It can be said as the current de-facto lingua franca of web programming. New language or framework that is based on javasript pop out left and right. The current hotstuff in javascript is of course React.js, Anguar.js, and Ember.js. We never know though what the future holds for these frameworks, since the web programming realm move at a really fast pace. Here is some of my favourite resource for learning Javascript
Actually, for Javascript, there are tonnes of resource available to learn from, so I wont be worrying about that once you already started learning Javascript. Just a quick google search and you will likely find what you want
ps: I cant wait for WebAssembly