When utilizing code similar to the one below, one would assume that TypeScript could infer that badObj is a valid argument for fn, as it should have the type Bad.
Interestingly, within the body of fn there seems to be no issue. However, when calling fn(badObj), an error occurs at the bottom. The same happens with fn(goodObj).
Is there a way to modify this code to achieve the expected behavior?
interface Ok {
ok: true;
date: undefined;
}
interface Bad {
ok: false;
date: Date;
}
const badObj = { ok: false, date: new Date()};
const goodObj = { ok: true, date: undefined}
const fn = (obj: Ok | Bad) => {
console.log(obj.ok);
if (!obj.ok) {
const minutes = obj.date.getMinutes();
}
};
fn(badObj)
fn(goodObj)
/*
The following error is thrown on the invocation of `fn(badObj)` and `fn(goodObj)`
Argument of type '{ ok: boolean; date: Date; }' is not assignable to parameter of type 'Ok | Bad'.
Type '{ ok: boolean; date: Date; }' is not assignable to type 'Bad'.
Types of property 'ok' are incompatible.
Type 'boolean' is not assignable to type 'false'.(2345)
*/
*/