Why doesn't the optional chaining operator (?.) work with Javascript assignment? [duplicate]

Question

When I do this:

  var resetButton = document.querySelector('.resetButton');
  resetButton?.onclick = function() {
   //...
  };

I got error: Uncaught SyntaxError: invalid assignment left-hand side.
I would like to be able to use optional chaining on every object.

I believe you are looking for the nullish coalescing assignment operator: ??=. Wrap the outer objects in something like ((foo ??= {}).bar ??= {}).baz ??= qux. — InSync
– InSync, Commented Jun 17, 2023 at 1:50
Counter-example: if the left-hand-side ?. expression evaluates to null, then should the right-hand-side expression still be evaluated... or not? I suspect that's the reason why it isn't supported (because if the right-hand-side has side-effects but the left-hand-side is null then that's probably a bug, so probably better to avoid that situation entirely). — Dai
– Dai, Commented Jun 17, 2023 at 1:51
@AlexT. JS added the ?. operator sometime around 2019-2020: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — Dai
– Dai, Commented Jun 17, 2023 at 1:52
Not actually "recently" per se, as browsers started supporting it three years ago. — InSync
– InSync, Commented Jun 17, 2023 at 1:53
@InSync It's still "recent" to me: the last 3 years have kinda been a blur for me... also, a major blocker for newer JS features is now Safari, as users with older iPhones will be stuck on older iOS + Safari versions - and you can't polyfill support for syntax features :/ — Dai
– Dai, Commented Jun 17, 2023 at 1:56

Gaurav Yadav · Accepted Answer · 2023-06-17 01:59:33Z

0

'?.' is used when you want to access something that may be undefined(no errors)?. does not return any reference so you can't use it to assign.

answered Jun 17, 2023 at 1:59

Gaurav Yadav

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