Does javascript have an optional indexing operator?

Question

Sometimes I have:

let a = { b: { c1: { z: false } } }

Other times I have:

let a = { b: { c2: { z: false } } }

I have let n = 'c1' or let n = 'c2'

I can do this to propagate the undefined:

a?.b[n]?.z

But other than if(a.b) ..., can I do anything shorthand if b is undefined?

There isn't a ?[ it seems, and I don't think I can do a['b'][n]?.z either, because if there is no b then attempting to index n on it will give cannot read property VALUE_OF_N of undefined ?

Answer 1

Yes:

a?.b?.[n]?.z

The ?. operator can be used before a [ ] expression. It looks odd, but ?. is itself a complete token so it syntactically makes sense. In other words, ?. normally isn't just a question mark before the usual . operator; it's an entire operator unto itself.

let a;
let n;

a = { b: { c1: { z: false } } }
n = 'c1';

console.log(a?.b[n]?.z);

a = { b: { c2: { z: false } } }
n = 'c2';

console.log(a?.b?.[n]?.z);