Function isInstanceOf

packages/forms/test/form_control_spec.ts:1646–1649

(value: Constructor<T>, arg: unknown)

      type Constructor<T> = Function & {prototype: T};

      function isInstanceOf<T>(value: Constructor<T>, arg: unknown): arg is T {
        // The implementation does not matter; we want to check whether this guard narrows the type.
        return true;
      }

      // This is a nullable FormControl, and we want isInstanceOf to narrow the type.
      const fcOrNull: FormControl | null = new FormControl(42);