public purchase(purchaseRequestParams: IAPTypes.PurchaseParams): Promise<PurchaseResponse>;

const triggerPurchase = (sku?: string): void => {
      Logger.debug(`Item ${sku} clicked`);
      PurchasingService.purchase({ sku: sku })
            .then((res) => {
               // Handle purchase response.
            })
            .then((user) => {
               // perform operation for user if required.
            })
            .catch((err) => {
               // Handle exceptions if any
            });

      return;
}

useEffect(() => { // Validate product SKUs before rendering product screen
      // ...

      // Calling getProductData when the component is rendered.
      PurchasingService.getProductData({ skus: Constants.SKUS })
         .then((res) => {
            const [productData, unavailableSkus] = handleProductDataResponse(res);
         })
         .catch((err) => {
            Logger.error(`Exception while calling getProductData ${err}`);
         });
   }, []);