no-unused-expressions makes an error for optional chaining of method calls: foo?.bar();

[Frozen-byte]

Reviving #11045 since optional chaining arrived Stage4!

I am unable to write a heads-up to the Issue itself.
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[kaicataldo]

We're currently blocked by estree/estree#204. Once that lands, all of the core rules will be updated to handle this syntax. Thanks for your patience!

[tom-sherman]

Slightly adjacent, what is the reason for the "no-unused-expressions" rule being matched for statements that cannot be parsed?

[kaicataldo]

My guess is that the issue author is using a custom parser that can parse this. When using the default parser, this would currently be a parser error.

[Frozen-byte]

Yes I am using "babel/no-unused-expressions" to get around that other issue.

[roth-j]

Has this issue been addressed? I am still seeing the eslint error for an unused expression when using optional chaining

class My Component {

...

  onChange = evt => {
    this.props.onChange?.(evt.target.value); // throws no-unused-expression
  }; 

  noChangeAlt = evt => {
    this.props.onChange(evt.target.value); // no eslint error but its complaining about executing a possibly undefined thing
  }

[garrettg123]

In the meantime, you can ignore with "no-unused-expressions": "off".

[kaicataldo]

As mentioned above, we're still blocked by ESTree deciding on the AST spec.

[tomasklingen]

estree/estree#204 is merged! :)

[jeiea]

Any update on this? We can remove blocked label at least.

[mdjermanovic]

The core no-unused-expressions rule will support optional chaining per the estree specification when we release #13416 (expected to be in v7.5.0).

At that point, the rule will work well with the default parser.

However, if you're using babel-eslint, the current version of babel-eslint parser generates a different AST so the rule will probably not work well until babel-eslint releases babel/babel#11815.

Until the new babel-eslint release, you should probably use babel-eslint-plugin and babel/no-unused-expressions rule instead of the core no-unused-expressions rule.

Edit: we changed how the core no-unused-expressions rule works (please see the comment bellow), so now it can be used with babel-eslint, too.

[jeiea]

#13416 and babel/babel#11815 seems to be released. I had no issue without babel-eslint-plugin. Can we close this issue?

[mdjermanovic]

Yes, I think we can close this issue.

We also changed the rule to not warn on unknown expressions when used with third-party parsers.

I can confirm now that the core no-unused-expressions rule doesn't report an error on foo?.bar(); when used with any of the following parsers: espree (default parser), babel-eslint, @babel/eslint-parser, @typescript-eslint/parser.