Which truthy values have no property?

Question

I am trying to write the shortest readable code to access the property of a variable that I have no information about, but I want this property access to be safe:

const x = getXSomehow();

const y = x.z; // 1
const y = x?.z; // 2
const y = x != null && x.z; // 3
const y = x && x.z; // 4

Might throw if x is null or undefined
Would be perfect, but I can't use optional chaining (for some reason out of the scope of this question)
Works & is used by other libraries like lodash and coffeescript to access props in a null safe way, but reads ugly
I wanna use this, but this would fail if there exist something truthy in JS that doesn't let you access its properties - can this even happen? All I can think of is null and undefined, but perhaps there exist an exotic JS value that is both truthy and throws on property access

I'd take a closer look at 2. If browser compatibility is the issue, could you integrate Babel into your build process (it should already be present anyway, in a reasonably professional project IMO), and then use optional chaining, and have it transpiled down to ES5/ES2015 for production? (if not, OK, but that's what I'd do) — CertainPerformance, Feb 18 '21 at 16:34
Nope, that's an issue with babel + jest + istanbul that doesn't handles optional chaining, I mean it could theoretically, but our team collectively decided that this work would be too costly! But yes I would agree if it wasn't for that detail — Nino Filiu, Feb 18 '21 at 16:47

score 1 · Answer 1 · answered Feb 18 '21 at 16:41

this would fail if there exist something truthy in JS that doesn't let you access its properties - can this even happen?

It could, but it'd be pretty strange - like a getter that may throw:

const obj = {
  get prop() {
    throw new Error();
  }
};

console.log(obj.prop);

Or a Proxy with the same sort of thing.

But this same method would result in each method throwing - all of 1, 2, 3, and 4; it's too strange to be worth worrying about in normal code, I think.

If it were me, I'd re-examine (2) to see whether it'd be at all possible to change your build process to integrate optional chaining. Otherwise, you'll have to choose between (3) and (4).

Which truthy values have no property?

1 Answers1