persist preferred lang across pages and refresh

Author: davemooreuws

src/hooks/useLang.ts

@@ -25,6 +25,8 @@ export type LanguageId =
 
 const languages = ['javascript', 'python', 'go', 'typescript', 'dart']
 
+const LOCAL_STORAGE_KEY = 'nitric.docs.selected.language'
+
 const useLang = () => {
   const searchParams = useSearchParams()
 
@@ -52,13 +54,34 @@ const useLang = () => {
       const query = search ? `?${search}` : ''
 
       window.history.pushState(null, '', query)
+
+      if (query) {
+        // set language in local storage
+        try {
+          localStorage.setItem(LOCAL_STORAGE_KEY, id)
+        } catch (e) {
+          // ignore
+        }
+      }
     },
     [searchParams],
   )
 
   useEffect(() => {
     // add data current lang to body to style based on language, used in hide/show blocks
     document.body.dataset.currentLang = currentLanguage
+
+    // set query params from local storage if no query params are present
+    if (!queryParamLang) {
+      const localLang = localStorage.getItem(LOCAL_STORAGE_KEY) as LanguageId
+      if (
+        localLang &&
+        languages.includes(localLang) &&
+        localLang !== currentLanguage
+      ) {
+        setLanguage(localLang)
+      }
+    }
   }, [currentLanguage])
 
   return {