John Carmack on mutable variables

One area that I like to have immutability is in function argument passing. In javascript (and many other languages), I find it weird that arguments in function act differently depending on if they are simple (strings, numbers) versus if they are complex (objects, arrays).

I want everything that passes through a function to be a copy unless I put in a symbol or keyword that it suppose to be passed by reference.

I made a little function to do deep copies but am still experimenting with it.

  function deepCopy(value) {
    if (typeof structuredClone === 'function') {
      try { return structuredClone(value); } catch (_) {}
    }
    try {
      return JSON.parse(JSON.stringify(value));
    } catch (_) {
      // Last fallback: return original (shallow)
      return value;
    }
  }