interface Car { manufacturer: string, } interface City { population: number, } const arr: (City | Car)[] = [{ population: 100 }, { manufacturer: 'ABC' }]; const filteredArr = arr.filter((item) => 'manufacturer' in item); // ??
filteredArr
const filteredArr = arr.filter((item): item is Car => 'manufacturer' in item); // filteredArr now has Car[] type