refactor: complete utils/display.ts tests and docs

routes/pricing.tsx

@@ -8,7 +8,7 @@ import {
   stripe,
   StripProductWithPrice,
 } from "@/utils/stripe.ts";
-import { formatAmountForDisplay } from "@/utils/display.ts";
+import { formatCurrency } from "@/utils/display.ts";
 import Stripe from "stripe";
 import IconCheckCircle from "tabler_icons_tsx/circle-check.tsx";
 import Head from "@/components/Head.tsx";
@@ -83,7 +83,7 @@ function PremiumPlanCard(
         </div>
         <p>
           <span class="text-4xl font-bold">
-            {formatAmountForDisplay(
+            {formatCurrency(
               defaultPrice.unit_amount! / 100,
               defaultPrice?.currency,
             )}

utils/display.ts

@@ -10,7 +10,6 @@ import { difference } from "std/datetime/difference.ts";
  *
  * pluralize(0, "meow"); // Returns "0 meows"
  * pluralize(1, "meow"); // Returns "1 meow"
- * pluralize(2, "meow"); // Returns "2 meows"
  * ```
  */
 export function pluralize(amount: number, unit: string) {
@@ -26,7 +25,6 @@ export function pluralize(amount: number, unit: string) {
  * import { SECOND, MINUTE, HOUR } from "std/datetime/constants.ts";
  *
  * timeAgo(new Date()); // Returns "just now"
- * timeAgo(new Date(Date.now() - MINUTE)); // Returns "2 minutes ago"
  * timeAgo(new Date(Date.now() - 3 * HOUR)); // Returns "3 hours ago"
  * ```
  */
@@ -55,18 +53,33 @@ export function timeAgo(date: Date) {
   return pluralize(amount, unit.slice(0, -1)) + " ago";
 }
 
-export function formatAmountForDisplay(
+/**
+ * Returns a formatted string based on the given amount of currency and the
+ * machine's preferred language.
+ *
+ * @see {@linkcode Intl.NumberFormat}
+ *
+ * @example
+ * ```ts
+ * import { formatCurrency } from "@/utils/display.ts";
+ *
+ * formatCurrency(4, "USD"); // Returns "$5"
+ * ```
+ */
+export function formatCurrency(
   amount: number,
   currency: string,
 ): string {
-  const numberFormat = new Intl.NumberFormat(
+  return new Intl.NumberFormat(
     navigator.language,
     {
       style: "currency",
       currency,
       currencyDisplay: "symbol",
       maximumFractionDigits: 0,
     },
-  );
-  return numberFormat.format(amount);
+  ).format(amount)
+    // Issue: https://stackoverflow.com/questions/44533919/space-after-symbol-with-js-intl
+    .replace(/^(\D+)/, "$1")
+    .replace(/\s+/, "");
 }

utils/display_test.ts

@@ -1,7 +1,7 @@
 // Copyright 2023 the Deno authors. All rights reserved. MIT license.
-import { pluralize, timeAgo } from "./display.ts";
+import { formatCurrency, pluralize, timeAgo } from "./display.ts";
 import { DAY, HOUR, MINUTE, SECOND } from "std/datetime/constants.ts";
-import { assertEquals } from "std/assert/mod.ts";
+import { assertEquals, assertThrows } from "std/assert/mod.ts";
 
 Deno.test("[display] pluralize()", () => {
   assertEquals(pluralize(0, "item"), "0 items");
@@ -24,4 +24,13 @@ Deno.test("[display] timeAgo()", () => {
   assertEquals(timeAgo(new Date(Date.now() - DAY)), "1 day ago");
   assertEquals(timeAgo(new Date(Date.now() - DAY - HOUR * 12)), "1 day ago");
   assertEquals(timeAgo(new Date(Date.now() - DAY * 5)), "5 days ago");
+  assertThrows(
+    () => timeAgo(new Date(Date.now() + 1)),
+    Error,
+    "Timestamp must be in the past",
+  );
+});
+
+Deno.test("[display] formatCurrency()", () => {
+  assertEquals(formatCurrency(5, "USD"), "$5");
 });