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Plain JS tests are in $ts/tests/cases/conformance/salsa/plainJS*. You can get the settings you need to test them from the existing tests.

A couple of gotchas I thought of:

• "[object Object]" == {}
• { toString() { return 'hi' }, valueOf() { return 'no' } } == { toString() { return 'no' }, valueOf() { return 'hi' } }

At least, I think there are shenanigans possible with valueOf; I couldn't get a working example.

I think there's no need to support the first case. The second case is a bit more interesting, maybe I can add detection to check if the literal contains toString, valueOf, or any computed property name only in JS.

Add test files.

A couple more examples from Brad Zacher (@bradzacher)'s comment:

[1,2,3] == '1,2,3'
// -> true

({toString() { return 1 }}) == 1
// -> true

The second one is pretty close to the second example in my comment but arguably more likely to be written as a weird workaround for something. Even a weird workaround shouldn't have an error in JS given the reaction of some JS users when an unavoidable red squiggly shows up.

So we only emit it for === not for ==?

Yeah, I think so.

done

rebased