formatted useLocalesMap error and added additional checks

Author: valentinpolitov

components/use-locales-map.js

@@ -5,38 +5,64 @@ import { useRouter } from "next/router";
  * @typedef {DefaultLocale | "zh-CN" | "es-ES" | "pt-BR" | "ja" | "ko" | "ru"} Locale
  * @typedef {{locale?: Locale | undefined; locales?: Locale[] | undefined; defaultLocale?: DefaultLocale | undefined}} TypedRouter
  * @typedef {Omit<import('next/router').NextRouter, "locale" | "locales" | "defaultLocale"> & TypedRouter} NextRouter
+ */
+
+/**
  * @template T
  * @type {(localesMap: Record<Locale, T>) => T}
  */
 export default function useLocalesMap(localesMap) {
   /** @type {NextRouter} */
   const router = useRouter();
-  const { locale, defaultLocale } = router;
+  const { locale, locales, defaultLocale } = router;
 
   if (!localesMap) {
-    throw new Error("Pass a locales map as argument to useLocalesMap");
+    throw new Error("Pass a locales map as argument to useLocalesMap hook.");
   }
 
-  if (!isObject(localesMap)) {
-    throw new Error("Locales map must be an object");
+  if (typeof localesMap !== "object") {
+    localesMapError(
+      localesMap,
+      `Locales map must be an object, but you passed ${typeof localesMap}.`
+    );
+  }
+
+  if (Array.isArray(localesMap)) {
+    localesMapError(
+      localesMap,
+      "Locales map must be an object, but you passed an array."
+    );
   }
 
   if (!localesMap.hasOwnProperty(defaultLocale)) {
-    throw new Error(
+    localesMapError(
+      localesMap,
       `Locales map must contain default locale "${defaultLocale}"`
     );
   }
 
-  if (
-    localesMap.hasOwnProperty(locale) &&
-    typeof localesMap[locale] !== typeof localesMap[defaultLocale]
-  ) {
-    throw new Error(
-      `Invalid locales map: Shape of "${locale}" must be the same as "${defaultLocale}"`
-    );
+  for (const key in localesMap) {
+    if (!locales.includes(key)) {
+      const list = locales.map((l) => `"${l}"`).join(", ");
+
+      localesMapError(
+        localesMap,
+        `"${key}" is not a valid locale.`,
+        `Available locales are defined in "next.config.js": ${list}.`
+      );
+    }
+
+    if (typeof localesMap[key] !== typeof localesMap[defaultLocale]) {
+      localesMapError(
+        localesMap,
+        `Shape of "${key}" must be the same as "${defaultLocale}"`
+      );
+    }
   }
 
-  if (["string", "number", "symbol"].includes(typeof localesMap[defaultLocale])) {
+  if (
+    ["string", "number", "symbol"].includes(typeof localesMap[defaultLocale])
+  ) {
     return localesMap[locale] || localesMap[defaultLocale];
   }
 
@@ -76,3 +102,17 @@ export function mergeDeep(target, ...sources) {
 
   return mergeDeep(target, ...sources);
 }
+
+/**
+ * Throw an error with a formatted message.
+ * @template T
+ * @param {Record<Locale, T>} localesMap
+ * @param  {string[]} args
+ */
+export function localesMapError(localesMap, ...args) {
+  throw new Error(
+    ["Invalid locales map", JSON.stringify(localesMap, null, 2), ...args].join(
+      "\n"
+    )
+  );
+}