John Carmack on mutable variables

In JavaScript, I really like const and have adopted this approach. There are some annoying situations where it doesn't work though, to do with scoping. Particularly:

- if (x) { const y = true } else { const y = false } // y doesn't exist after the block - try { const x = foo } catch (e) { } // x doesn't exist after the try block

JavaScript’s `const` has the bigger issue that while things can’t be reassigned, they can still mutate. For example:

  const myArray = [1,2,3]
  myArray.push(4)
  myArray // [1, 2, 3, 4]

In what way is that an issue?

Because this isn't immutability. The goal is to have a way to define an object that will never change after initialisation, and JS's const isn't it.

Clearly that isn't the goal.