feat: strongly typed session storage usage

support-frontend/assets/pages/[countryGroupId]/checkout/helpers/sessionStorage.ts

@@ -1,32 +1,42 @@
 import { storage } from '@guardian/libs';
-import { type InferInput, object, picklist, safeParse, string } from 'valibot';
+import type { InferInput } from 'valibot';
+import { is, object, picklist, safeParse, string } from 'valibot';
+
+function fromSessionStorage(
+	key: string,
+	schema: typeof OrderSchema | typeof ReturnAddressSchema,
+) {
+	const sessionStorage = storage.session.get(key);
+	const parsed = safeParse(schema, sessionStorage);
+	return parsed.success ? parsed.output : undefined;
+}
 
 /**
  * The Guardian Ad-Lite Landing Page sets the returnLink in sessionStorage
  * And the thank-you page reads it.
  */
-export const ReturnAddressSchema = object({
+const ReturnAddressSchema = object({
 	link: string(),
 });
-export function setReturnAddress(link: InferInput<typeof ReturnAddressSchema>) {
+type ReturnAddressSchemaType = InferInput<typeof ReturnAddressSchema>;
+export function setReturnAddress(link: ReturnAddressSchemaType) {
 	storage.session.set('returnAddress', link);
 }
-export function getReturnAddress() {
-	const sessionStorageReturnAddress = storage.session.get('returnAddress');
-	const parsedReturnAddress = safeParse(
+export function getReturnAddress(): string {
+	const parsedReturnAddress = fromSessionStorage(
+		'returnAddress',
 		ReturnAddressSchema,
-		sessionStorageReturnAddress,
 	);
-	return parsedReturnAddress.success
-		? parsedReturnAddress.output.link
+	return is(ReturnAddressSchema, parsedReturnAddress)
+		? parsedReturnAddress.link
 		: 'https://www.theguardian.com';
 }
 
 /**
  * The checkout page sets the order in sessionStorage
  * And the thank-you page reads it.
  */
-export const OrderSchema = object({
+const OrderSchema = object({
 	firstName: string(),
 	email: string(),
 	paymentMethod: picklist([
@@ -39,19 +49,14 @@ export const OrderSchema = object({
 	]),
 	status: picklist(['success', 'pending']),
 });
-export function setThankYouOrder(order: InferInput<typeof OrderSchema>) {
+type OrderSchemaType = InferInput<typeof OrderSchema>;
+export function setThankYouOrder(order: OrderSchemaType) {
 	storage.session.set('thankYouOrder', order);
 }
-export function getThankYouOrder() {
-	const sessionStorageOrder = storage.session.get('thankYouOrder');
-	const parsedOrder = safeParse(OrderSchema, sessionStorageOrder);
-	if (parsedOrder.success) {
-		return parsedOrder.output;
-	} else {
-		return undefined;
-	}
+export function getThankYouOrder(): OrderSchemaType | undefined {
+	const parsedOrder = fromSessionStorage('thankYouOrder', OrderSchema);
+	return is(OrderSchema, parsedOrder) ? parsedOrder : undefined;
 }
-
 export function unsetThankYouOrder() {
 	storage.session.remove('thankYouOrder');
 }