Removing Nullish Members with NonNullable

Removing Nullish Members with NonNullable: working example

Run this standalone example after compiling with TypeScript 5.4+ in strict mode, targeting ES2022. Expected result: The program prints 0,8; zero is preserved while null and undefined are removed.

function present<T>(value: T): value is NonNullable<T> {
  return value !== null && value !== undefined;
}
const values: (number | null | undefined)[] = [0, null, 4, undefined];
const numbers = values.filter(present);
console.log(numbers.map(value => value * 2).join(","));

1. Expected result: The program prints 0,8; zero is preserved while null and undefined are removed.
2. The explicit nullish comparisons avoid accidentally discarding zero.
3. The predicate connects runtime filtering to the NonNullable result type.