Port detect-language.js to TypeScript (#50623)

package.json

@@ -290,6 +290,7 @@
     "@graphql-tools/load": "^8.0.0",
     "@octokit/rest": "^20.1.0",
     "@playwright/test": "1.44.0",
+    "@types/accept-language-parser": "1.5.6",
     "@types/connect-datadog": "0.0.10",
     "@types/connect-timeout": "0.0.39",
     "@types/cookie": "0.6.0",

src/frame/middleware/index.ts

@@ -17,7 +17,7 @@ import {
 } from './set-fastly-surrogate-key.js'
 import handleErrors from '@/observability/middleware/handle-errors'
 import handleNextDataPath from './handle-next-data-path'
-import detectLanguage from '@/languages/middleware/detect-language.js'
+import detectLanguage from '@/languages/middleware/detect-language'
 import reloadTree from './reload-tree.js'
 import context from './context/context.js'
 import shortVersions from '@/versions/middleware/short-versions.js'

src/languages/middleware/detect-language.js → src/languages/middleware/detect-language.ts

@@ -1,7 +1,10 @@
-import languages, { languageKeys } from '#src/languages/lib/languages.js'
+import type { Request, Response, NextFunction } from 'express'
 import parser from 'accept-language-parser'
+import type { Language as parserLanguage } from 'accept-language-parser'
 
-import { USER_LANGUAGE_COOKIE_NAME } from '#src/frame/lib/constants.js'
+import languages, { languageKeys } from '@/languages/lib/languages.js'
+import { USER_LANGUAGE_COOKIE_NAME } from '@/frame/lib/constants.js'
+import type { ExtendedRequest, Languages } from '@/types'
 
 const chineseRegions = [
   'CN', // Mainland
@@ -10,25 +13,28 @@ const chineseRegions = [
   'TW', // Taiwan
 ]
 
-function translationExists(language) {
+function translationExists(language: parserLanguage) {
   if (language.code === 'zh') {
-    return chineseRegions.includes(language.region)
+    return language.region && chineseRegions.includes(language.region)
   }
   // 92BD1212-61B8-4E7A: Remove ` && !languages[language.code].wip` for the public ship of ko, fr, de, ru
-  return languageKeys.includes(language.code) && !languages[language.code].wip
+  return languageKeys.includes(language.code) && !(languages as Languages)[language.code].wip
 }
 
-function getLanguageCode(language) {
-  return language.code === 'cn' && chineseRegions.includes(language.region) ? 'zh' : language.code
+function getLanguageCode(language: parserLanguage) {
+  return language.code === 'cn' && language.region && chineseRegions.includes(language.region)
+    ? 'zh'
+    : language.code
 }
 
-function getUserLanguage(browserLanguages) {
+function getUserLanguage(browserLanguages: parserLanguage[]) {
   try {
     let numTopPreferences = 1
     for (let lang = 0; lang < browserLanguages.length; lang++) {
       // If language has multiple regions, Chrome adds the non-region language to list
-      if (lang > 0 && browserLanguages[lang].code !== browserLanguages[lang - 1].code)
+      if (lang > 0 && browserLanguages[lang].code !== browserLanguages[lang - 1].code) {
         numTopPreferences++
+      }
       if (translationExists(browserLanguages[lang]) && numTopPreferences < 3) {
         return getLanguageCode(browserLanguages[lang])
       }
@@ -38,26 +44,27 @@ function getUserLanguage(browserLanguages) {
   }
 }
 
-function getUserLanguageFromCookie(req) {
-  const value = req.cookies[USER_LANGUAGE_COOKIE_NAME]
+function getUserLanguageFromCookie(req: Request) {
+  const value: undefined | string = req.cookies[USER_LANGUAGE_COOKIE_NAME]
+
   // 92BD1212-61B8-4E7A: Remove ` && !languages[value].wip` for the public ship of ko, fr, de, ru
-  if (value && languages[value] && !languages[value].wip) {
+  if (value && (languages as Languages)[value] && !(languages as Languages)[value].wip) {
     return value
   }
 }
 
 // determine language code from a path. Default to en if no valid match
-export function getLanguageCodeFromPath(path) {
+export function getLanguageCodeFromPath(path: string) {
   const maybeLanguage = (path.split('/')[path.startsWith('/_next/data/') ? 4 : 1] || '').slice(0, 2)
   return languageKeys.includes(maybeLanguage) ? maybeLanguage : 'en'
 }
 
-export function getLanguageCodeFromHeader(req) {
+export function getLanguageCodeFromHeader(req: Request) {
   const browserLanguages = parser.parse(req.headers['accept-language'])
   return getUserLanguage(browserLanguages)
 }
 
-export default function detectLanguage(req, res, next) {
+export default function detectLanguage(req: ExtendedRequest, res: Response, next: NextFunction) {
   req.language = getLanguageCodeFromPath(req.path)
   // Detecting browser language by user preference
   req.userLanguage = getUserLanguageFromCookie(req)

src/types.ts

@@ -10,5 +10,19 @@ export type ExtendedRequest = Request & {
     currentCategory?: string
     error?: Error
   }
+  language?: string
+  userLanguage?: string
   // Add more properties here as needed
 }
+
+type Language = {
+  name: string
+  code: string
+  hreflang: string
+  dir: string
+  wip: boolean
+}
+
+export type Languages = {
+  [key: string]: Language
+}