Support server side rendering in useLocalStorage

I've added some simple `if (typeof window === "undefined")` clauses around the `localStorage` calls.

Don't know if there's a policy around this, but I'm betting a lot of people use these hooks in Next.js and I figured this could be helpful.

Author: fredrikekelund

src/pages/useLocalStorage.md

@@ -40,6 +40,10 @@ function useLocalStorage(key, initialValue) {
   // State to store our value
   // Pass initial state function to useState so logic is only executed once
   const [storedValue, setStoredValue] = useState(() => {
+    if (typeof window === "undefined") {
+      return initialValue;
+    }
+
     try {
       // Get from local storage by key
       const item = window.localStorage.getItem(key);
@@ -62,7 +66,9 @@ function useLocalStorage(key, initialValue) {
       // Save state
       setStoredValue(valueToStore);
       // Save to local storage
-      window.localStorage.setItem(key, JSON.stringify(valueToStore));
+      if (typeof window !== "undefined") {
+        window.localStorage.setItem(key, JSON.stringify(valueToStore));
+      }
     } catch (error) {
       // A more advanced implementation would handle the error case
       console.log(error);
@@ -98,6 +104,10 @@ function useLocalStorage<T>(key: string, initialValue: T) {
   // State to store our value
   // Pass initial state function to useState so logic is only executed once
   const [storedValue, setStoredValue] = useState<T>(() => {
+    if (typeof window === "undefined") {
+      return initialValue;
+    }
+
     try {
       // Get from local storage by key
       const item = window.localStorage.getItem(key);
@@ -120,7 +130,9 @@ function useLocalStorage<T>(key: string, initialValue: T) {
       // Save state
       setStoredValue(valueToStore);
       // Save to local storage
-      window.localStorage.setItem(key, JSON.stringify(valueToStore));
+      if (typeof window !== "undefined") {
+        window.localStorage.setItem(key, JSON.stringify(valueToStore));
+      }
     } catch (error) {
       // A more advanced implementation would handle the error case
       console.log(error);