@automattic/calypso-products/src/is-jetpack-legacy-item.ts

This module contains information about the various products sold within calypso, such as product slugs, plan intervals, etc.

import { JETPACK_LEGACY_PLANS } from './constants';
import type { JetpackLegacyPlanSlug } from './types';

export default function isJetpackLegacyItem( itemSlug: string ): itemSlug is JetpackLegacyPlanSlug {
	return JETPACK_LEGACY_PLANS.includes( itemSlug as JetpackLegacyPlanSlug );
}