TypeScript: typesafe array filtering for null

typesafe-array-null-filter.ts

"https://www.typescriptlang.org/play?target=7#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"

interface Car {
  id: number;
  model: string | null
}

const car1: Car | null = { id: 1, model: "A" }
const car2: Car | null = null
const car3: Car | null = { id: 3, model: "C" }

const cars: (Car | null)[] = [car1, car2, car3]

let carsWithoutNull: Car[] = []

// with .filter (error: "Type 'null' is not assignable to type 'Car'.")
carsWithoutNull = cars.filter(car => car !== null)

// with .filter + defining type (hacky, same problem like using "as")
carsWithoutNull = cars.filter((car): car is Car => car !== null);

// with .reduce
carsWithoutNull = cars.reduce<Car[]>((acc, car) => (
  !car ? acc : [...acc, car]
), [])

// with .flatMap
carsWithoutNull = cars.flatMap(car => !car ? [] : [car]);