Minority opinion: please `let` your mutable references. I know `const` doesn’t signal immutability, but we as humans with eyeballs and limited attention span certainly benefit from knowing when a value might change at runtime.

Disagree: virtually everything in JS is mutable, so this almost means "never use the `const` keyword". Pretending that the `const` keyword means something that it doesn't makes things harder for my limited human mind to understand, not easier. Plus using `let` inappropriately makes my linter yells at me, and I usually like to just do whatever my linter tells me.

Anyway, I use TypeScript, so if I really want to assert that my array is immutable (as immutable as stuff in JS-land gets anyway) I just write:

  const input: readonly number[] = [1, 2, 3, 4, 5];

or even

  const input = [1, 2, 3, 4, 5] as const;

I realize I could be clearer in what I’m asking for: please use const when you use reference types as values, and use let when you intend to mutate the reference. Using const and then changing a value is certainly allowed but it’s confusing and it’s missing an opportunity to signal in the code where changes might happen.

I `readonly` and `as const` everything I possibly can. I do know that const doesn’t mean immutable, as I said, but I think it should and I think there’s value in establishing the idiom even if it’s not currently adopted. Because otherwise const basically means nothing unless you’re mutating everything already.