darkTheme in localStorage

webUI/react/src/util/useLocalStorage.tsx

@@ -0,0 +1,42 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+import { useState, Dispatch, SetStateAction } from 'react';
+
+// eslint-disable-next-line max-len
+export default function useLocalStorage<T>(key: string, initialValue: T) : [T, Dispatch<SetStateAction<T>>] {
+    // State to store our value
+    // Pass initial state function to useState so logic is only executed once
+    const [storedValue, setStoredValue] = useState<T>(() => {
+        try {
+        // Get from local storage by key
+            const item = window.localStorage.getItem(key);
+
+            // Parse stored json or if null return set and return initialValue
+            if (item !== null) { return JSON.parse(item); }
+
+            window.localStorage.setItem(key, JSON.stringify(initialValue));
+        } finally {
+            // eslint-disable-next-line no-unsafe-finally
+            return initialValue;
+        }
+    });
+
+    // Return a wrapped version of useState's setter function that ...
+    // ... persists the new value to localStorage.
+    const setValue = (value: T | ((prevState: T) => T)) => {
+        try {
+        // Allow value to be a function so we have same API as useState
+            const valueToStore = value instanceof Function ? value(storedValue) : value;
+            // Save state
+            setStoredValue(valueToStore);
+            // Save to local storage
+            window.localStorage.setItem(key, JSON.stringify(valueToStore));
+
+        // eslint-disable-next-line no-empty
+        } catch (error) { }
+    };
+
+    return [storedValue, setValue];
+}