is better to use the === instead of ==, for prevent the coersion

I always forget about filter!

i guess it isn't the best practice

i wouldn't call this best practice do

It's created as a property of lexicalEnvironment object of function. This object is hidden. We don't have access to that object directly.
ECMAScript® 2020 Language Specification => 8.1 Lexical Environments

For starters:

• % is a general purpose remainder operator, while & is a bitwise operator. It wouldn't be surprising for bitwise operations to be faster than general purpose remainder operations (think of C).
• Don't use == to compare with 0, use ===. It's also slightly faster because of the lack of type checking and conversion

Probably a for loop. But the performance gain is probably also trivial, and for loops are less readable because it represents steps rather than logic.

I would like to ask is that really faster - creating function within function than simple for loop ?

What keeps getSecret from being called on createSecretHolder's invocation?

nice and neat,dude

Using function's activation object in order to get and set the 'secret' value. Clever indeed.