Even if you use CoffeeScript, you will need to learn javascript, and for everything that you write in CoffeeScript, you should know exactly how it will look when is compiled.So, if you learn CoffeeScript, you must also learn Babel, because it is ES6. If you write CoffeeScript, only people that use CoffeeScript will be able to read your code fluently. If you learn Babel instead, people will organic