Discussed a bit with @jamiebuilds offline. Some key scenarios and questions to resolve:

declare const ra: Record<string, any>;
if (Object.hasOwn(ra, "foo")) {
  ra.foo; // should be 'any'
}

declare const ru: Record<string, unknown>;
if (Object.hasOwn(ra, "foo")) {
  ra.foo; // should be 'unknown'
}

declare const abcd: { a: string, b: string } | { c: string, d: string };
if (Object.hasOwn(abcd, "a")) {
  abcd.b; // should be OK
}
// Should this be OK?
// Could argue either way
Object.hasOwn(abcd, "efg")

// TODO: Add more use cases + desired behavior

Support for Object.hasOwn (lib.d.ts and narrowing) #44253

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DanielRosenwasseropenedon May 25, 2021

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Support for `Object.hasOwn` (`lib.d.ts` and narrowing) #44253

DanielRosenwasser
openedon May 25, 2021