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Confusing rules around function parameter names in a type #53933
Description
Activity
The change between origin/release-4.8 and origin/release-5.0 occurred at 3b45f4d.
Reacted by Ryan CavanaughThat looks like… a valid destructuring, I think? The function takes an
IPaginatedParamsobject as its second argument and then destructures it, extracting thefirstandafterproperties from it. It is kind of weird to do that in a function type though, since there’s no function body to use the extracted properties—all that matters there is theIPaginatedParamsannotation.Looks like an unintended consequence. Bisects to #49089
Minimal:
// Should syntax error type Foo = ({ first = 0 }: { first?: number }) => unknown;
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on Oct 22, 2025
Bug Report
In auditing some code, I've noticed something that doesn't seem like it should compile. In >=4.95, the following code compiles without an issue, but in <=4.7.4, there is an error. Why is it possible to specify an object for the name of a parameter? This code was likely the result of a bad copy/paste, but TS isn't erroring on it. Am I missing something about the syntax? Also, is the discrepancy between versions intended?
Playground links for 4.7.4 vs 4.9.5
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