Composing TypeScript type guards

type-guard-composition.ts

/**
 * Type representing a guard function accepting Input and some other arguments
 * while refining type of input as `Output`
 */
export type TypeGuard<
  Input,
  Output extends Input,
  Args extends unknown[] = []
> = (value: Input, ...args: Args) => value is Output;

/**
 * Combines multiple TypeGuards using `&&` operator
 */
export function and<I, O extends I, O2 extends O, A extends unknown[] = []>(
  f: TypeGuard<I, O, A>,
  g: TypeGuard<O, O2, A>
): TypeGuard<I, O2, A> {
  return (value: I, ...args: A): value is O2 =>
    f(value, ...args) && g(value, ...args);
}
/**
 * Combines multiple TypeGuards using `||` operator
 */
export function or<I, O extends I, O2 extends O, A extends unknown[] = []>(
  f: TypeGuard<I, O, A>,
  g: TypeGuard<I, O2, A>
): TypeGuard<I, O | O2, A> {
  return (value: I, ...args: A): value is O | O2 =>
    f(value, ...args) || g(value, ...args);
}

another alternative https://gist.github.com/karol-majewski/237b73aaa34c7a38e44c20a3bb18a069

current version has this issue https://gist.github.com/safareli/73e833ca2dff84806f79e935b4b7e9c2