add MaintainAttrs hook

assets/js/app.js

@@ -25,9 +25,13 @@ import 'phoenix_html'
 import { Socket } from 'phoenix'
 import { LiveSocket } from 'phoenix_live_view'
 import topbar from '../vendor/topbar'
+import MaintainAttrs from './maintain_attrs'
 
 const csrfToken = document.querySelector("meta[name='csrf-token']").getAttribute('content')
-const liveSocket = new LiveSocket('/live', Socket, { params: { _csrf_token: csrfToken } })
+const liveSocket = new LiveSocket('/live', Socket, {
+  params: { _csrf_token: csrfToken },
+  hooks: { MaintainAttrs }
+})
 
 // Show progress bar on live navigation and form submits
 topbar.config({ barColors: { 0: '#29d' }, shadowColor: 'rgba(0, 0, 0, .3)' })