At some level, it will be interesting for you to take a closer look at the work done by TC39 which is the group responsible for the specification of the language 💖. To better understand what TC39 is as well as the role of the different members composing this group I invite you to listen to the following talk (or the one from the previous year).
It is for example possible to follow the next features that will arrive in JavaScript thanks to the following git repo. The entirety of the proposals follows a well-defined process that is described here.
If you want to learn how to read and understand the ECMAScript specification, I invite you to read the following articles from the V8 team.
Other links: