Type parameters constrained to type alias of generic class can't be used with instanceof - TypeScript 4.8 regression #49937
Description
Bug Report
🔎 Search Terms
generic type parameters type aliases generic classes instanceof
🕗 Version & Regression Information
- This changed between versions 4.7.3 and 4.8-beta
⏯ Playground Link
Playground link with relevant code
💻 Code
// If Table is non generic error does not occur
declare class TableClass<S = any> {
_field: S
}
export type Table = TableClass;
function fn<T extends Table>(o: T) {
return o instanceof TableClass // error in 4.8
}
declare const o: Table;
o instanceof TableClass // This is ok 🙁 Actual behavior
o instanceof TableClass causes an error when o is typed as a generic type parameter constrained to Table but not when o is typed as Table. This behavior is different in 4.7 and 4.8. In 4.7 neither of these was an error.
🙂 Expected behavior
o instanceof TableClass is valid in both cases