Save room shared keys to local storage

Signed-off-by: Šimon Brandner <simon.bra.ag@gmail.com>

src/useLocalStorage.ts

@@ -0,0 +1,59 @@
+/*
+Copyright 2023 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import EventEmitter from "events";
+import { useCallback, useEffect, useState } from "react";
+
+type LocalStorageItem = ReturnType<typeof localStorage.getItem>;
+
+// Bus to notify other useLocalStorage consumers when an item is changed
+export const localStorageBus = new EventEmitter();
+
+// Like useState, but reads from and persists the value to localStorage
+export const useLocalStorage = (
+  key: string
+): [LocalStorageItem, (value: string) => void] => {
+  const [value, setValue] = useState<LocalStorageItem>(() =>
+    localStorage.getItem(key)
+  );
+
+  useEffect(() => {
+    localStorageBus.on(key, setValue);
+    return () => {
+      localStorageBus.off(key, setValue);
+    };
+  }, [key, setValue]);
+
+  return [
+    value,
+    useCallback(
+      (newValue: string) => {
+        setValue(newValue);
+        localStorage.setItem(key, newValue);
+        localStorageBus.emit(key, newValue);
+      },
+      [key, setValue]
+    ),
+  ];
+};
+
+export const getLocalStorageItem = (key: string): LocalStorageItem =>
+  localStorage.getItem(key);
+
+export const setLocalStorageItem = (key: string, value: string): void => {
+  localStorage.setItem(key, value);
+  localStorageBus.emit(key, value);
+};