Should delete a?.b be allowed or forbidden?

[claudepache]

The right semantics of delete a?.b is evident and requires practically zero effort to spec. Should it be allowed or not?

[ljharb]

Deletion is strange enough; I'm not sure why we would want conditional deletion. We shouldn't be striving to add optional chaining everywhere it's possible imo; only where it's useful.

[rattrayalex]

Agreed with @ljharb .

delete a?.b seems like the kind of thing I would immediately write a linter rule to prevent if I ever saw it in the wild; it sounds like sloppy code for a case that shouldn't be encouraged. Furthermore, if I ever had an inclination to write it, I don't think I would expect it to work (at least, I would check "the docs", but I wouldn't assume either way).

[jridgewell]

Babel itself could benefit from optional deletion: https://github.com/babel/babel/blob/28ae47a174f67a8ae6f4527e0a66e88896814170/packages/babel-helper-builder-react-jsx/src/index.js#L66-L69

Not every parser adds the extra object to Node, and babylon doesn't necessarily need to do it either.

[ljharb]

That there exists a use case isn't necessarily a reason to add the feature :-)

[claudepache]

Thanks for the use case.

I expect to provisionally keep the “optional delete” feature when resolving #13 (but this Issue will remain open until a final decision is made).

[claudepache]

After careful consideration, I think that delete a?.b must be allowed, because:

• it is consistent with delete a.b not throwing when a evaluates to, say, a String;
• it has a reasonable use case;
• its semantics is not confusing.

Or said the other way, forbidding that form, will introduce an inconsistency in the semantics of delete (which is very permissive, even in strict mode), will prevent a reasonable use case, and won’t resolve any real issue.

[claudepache]

The ongoing refactoring of Issue #20 will imply that optional delete will be implemented even without changing a jot in the current specification of the delete operator. Disallowing it would be artificial. So, in absence of strong reason for forbidding, I am closing this issue.

[caub]

I don't think delete should be supported if assignment is not (either mutations are supported or not, for consistency)

const o={foo: 1}: o?.foo=undefined; o

is not supported as I see

But I'd rather not support both of them (#18)