In this post I propose to talk about ES6. ES6 gave us a lot of features that are definitely very cool. For me, these are a "map", "set", "weak map", "weak set", some functional programming elements (new.target, Symbol.species, etc), Symbol, the spread operator and possibility to use it for breaking strings into tokens. But in this post, I want to talk about those main features of es6, which, in my opinion, have small downsides.