NonNullable.tsx

type OtherComponentProps = {
  // ...
  onChange?: (value: number) => void;
};

// -----

const Component = () => {
  // We know for sure it's not nullable as we're initialising it, but TypeScript doesn't so we have to help it.
  const changeValue = useCallback<NonNullable<OtherComponentProps["onChange"]>>(
    (value) => {
      if (value > 0) {
        doSomethingWithTheValue(value);
      }
    },
    []
  );
  return <SomeOtherComponent onChange={changeValue} />;
};