feature: sync multiple tabs using local storage

lib/frontend/components/AppContainer.svelte

@@ -4,8 +4,6 @@
   import { configStore } from '../stores'
 
   $: showTrackingPanel = $configStore.track === undefined
-
-  configStore.subscribe(console.log)
 </script>
 
 {#if showTrackingPanel}

lib/frontend/index.js

@@ -1,8 +1,12 @@
 import App from './components/App.svelte'
 
 import * as stores from './stores'
+import * as services from './services'
 
 const boot = () => {
+
+  services.storageListener.register()
+
   new App({
     target: document.querySelector('#root'),
   })
@@ -10,6 +14,7 @@ const boot = () => {
   if (process.env.NODE_ENV === 'development') {
     window._fb2ical = {
       ...stores,
+      ...services,
     }
   }
 }

lib/frontend/services/index.js

@@ -0,0 +1,5 @@
+import storageListener from './storageListener'
+
+export {
+  storageListener,
+}

lib/frontend/services/storageListener.js

@@ -0,0 +1,45 @@
+import { configStore } from '../stores'
+
+const STORAGE_KEYS = {
+  CONFIG: 'fb-to-ical-config',
+}
+
+class StorageListener {
+  constructor() {
+    this._storeSubscribers = new Set()
+  }
+
+  register() {
+    window.addEventListener('storage', this._handleStorageChange)
+
+    const unsubscribeConfigStore = configStore.subscribe(this._handleConfigStoreChange)
+
+    this._storeSubscribers = new Set([
+      ...this._storeSubscribers,
+      unsubscribeConfigStore,
+    ])
+  }
+
+  unregister() {
+    window.removeEventListener('storage', this._handleStorageChange)
+
+    this._storeSubscribers.forEach((unsubscribe) => unsubscribe())
+    this._storeSubscribers.clear()
+  }
+
+  _handleStorageChange(event) {
+    switch (event.key) {
+      case STORAGE_KEYS.CONFIG:
+        configStore.set(JSON.parse(event.newValue))
+        break
+      default:
+        return
+    }
+  }
+
+  _handleConfigStoreChange(value) {
+    localStorage.setItem(STORAGE_KEYS.CONFIG, JSON.stringify(value))
+  }
+}
+
+export default new StorageListener()

lib/frontend/stores/configStore.js

@@ -6,24 +6,18 @@ const createConfigStore = () => {
   const { subscribe, set, update } = writable(state)
 
   const setValue = (key, value) => {
-    update((prevState) => {
+    update((prevState) => ({ ...prevState, [key]: value }))
-      const nextState = {
-        ...prevState,
-        [key]: value,
-      }
-
-      localStorage.setItem('fb-to-ical-config', JSON.stringify(nextState))
-
-      return nextState
-    })
   }
 
+  const getState = () => state
+
   return {
     ...state,
     subscribe,
     set,
     update,
     setValue,
+    getState,
   }
 }