Where can I find more ready-made solutions for this type?

Question

JavaScript

Hi, I’ll make a reservation right away that the question may seem ridiculous, because. The wording in my head is not very clear.
I study js and when I solved various kinds of problems in the solution examples I found the following universal elements:
1) for example, if we need a variable to increase by a certain value during the cycle and not forget its previous value, but it was written like this:
let num = 0;
for(let i=0; i<10; i++){
num+=i
} And I would not have thought of this myself num+=
2) When I was solving the fibonacci problem, I saw a solution where the counter in the loop was used to iterate over the elements of the array:
let num = [1,2,3,4,5];
for(let i=0; i<10; i++){
num[i]=....
} And again, I myself would not have thought of using it like that. These templates / tools help to solve various problems, but I don’t know where to find more such universal ready-made solutions? Most likely it's just the lack of flexibility of my brains, but still I wonder if there is such a place all in one place.
I just don't even know what they're called, just to google it. I really hope that you understand what I mean and help with the search.

Answer 1

Lack of knowledge of the basic features of the language. Study any modern JavaScript textbook from cover to cover. A good option learn.javascript.ru

Answer 2

in addition to the basics of JS, knowledge of algorithms will also come in handy