I'm a 55 year old senior developer. I've been coding since I was 12 (yeah, RPG II in punch cards and COBOL stored in 8" floppies), and I have a TERIBLE memory.
Don't bother memorizing and knowing every language feature and detail. Just get a general awareness of what it can do. Then when you need to accomplish something, it's good enough that for the first times you do it you go "hey, I recall there's a way of doing it" or at least (often happens to me) "hmm, this sounds useful enough that this language must have a built-in way of doing it". Then you google or ask some AI, and you'll get pointed to the general direction most of the times.
Then if you use it often enough, you'll remember it. (and in my case, if I don't use it for 3 months, I completely forget about it, and even get surprised when I see how I did it in my own old code).
In the old days, you could indeed know every feature and library (if any existed at all) of a language. Heck, I knew almost all hex op codes for the Z80 assembly by heart (still recall more of those than I recall my relatives names). Nowadays it is impossible to memorize everything.
In JS realm, if you look at the amount of components you have available in most frameworks, for example in UI5, or existing node modules for your node.js project, even trying to "memorize" them all is a waste of time. In cases like this, you just need to assume there's a component or module that does what you need, then be good at finding, choosing, and understanding how to use one.
Not to mention the reduntant stuff they throw in "modern" languages, like javascript's forEach. Some languages have 10 ways of doing the same thing, each one 0.1% more efficient for each particular case, but may catastrophically fail in some other specific case. Screw it. Learn the one that works well for every case and stick with it - you're not coding ultra performance critical stuff in js anyway.
Programming today is usually more an integration of functioning pieces than building from scratch (assuming that if you're talking about JavaScript, we're not talking about creating microcode for bare silicon).
Worry about building an efficient and robust logic in your head. Then the programming language is just a tool, way less important than the logic you came up with.
I see this, vlemmy.net!