Hacker News Reader

> I know that after reading a const line I don't have to check if someone rebinds this name before each use site -- it's impossible.

This turns out to be almost useless information for most of us, since the real problem is not re-assignment, but mutation of the value (in the case of non-primitives).

`const x = 2` feels great emotionally, but `const x = [2]` has the feeling of safety without any of the guarantee.

This is a classic case (quoted from Crockford regularly) of a utility that it sometimes useful and sometimes harmful (aka not useful), and there's a better option (`let`), so the better option should generally be preferred.

I only use `const` (refactor from `let`) when a piece of code is reasonably complete and I'm pretty sure re-assignment will not ever be appropriate. Guessing at that before writing the code is a premature optimization.

And guessing wrongly and having to refactor back to `let` later is more risky.

View on HN

const x = [5,6,7]; Object.observe(x, function(changes) { console.log('changes', changes); }); // ... // time to clear the array // WRONG! The code observing changes to the old x array will not see // this change or future changes to this new array. Because we used const, this // will trigger an error and immediately show us our mistake. x = []; // CORRECT. This mutates the array instead of creating a new empty array. x.length = 0;