Prevent multiple unsubscribe calls for ActionCable

app/assets/javascripts/channels/synchronized_editor_channel.js

@@ -42,6 +42,16 @@ $(document).on('turbolinks:load', function () {
         send_changes(delta, active_file) {
           const delta_with_user_id = {command: 'editor_change', current_user_id: current_user_id, active_file: active_file, delta: delta}
           this.perform('send_changes', {delta_with_user_id: delta_with_user_id});
+        },
+
+        is_connected() {
+          return App.cable.subscriptions.findAll(App.synchronized_editor.identifier).length > 0
+        },
+
+        disconnect() {
+          if (this.is_connected()) {
+            this.unsubscribe();
+          }
         }
       });
     }

app/assets/javascripts/editor/editor.js.erb

@@ -1089,8 +1089,8 @@ var CodeOceanEditor = {
         this.initializeDeadlines();
         CodeOceanEditorTips.initializeEventHandlers();
 
-        window.addEventListener("turbolinks:before-render", App.synchronized_editor?.unsubscribe.bind(App.synchronized_editor));
-        window.addEventListener("beforeunload", App.synchronized_editor?.unsubscribe.bind(App.synchronized_editor));
+        window.addEventListener("turbolinks:before-render", App.synchronized_editor?.disconnect.bind(App.synchronized_editor));
+        window.addEventListener("beforeunload", App.synchronized_editor?.disconnect.bind(App.synchronized_editor));
 
         window.addEventListener("turbolinks:before-render", this.autosaveIfChanged.bind(this));
         window.addEventListener("beforeunload", this.autosaveIfChanged.bind(this));

app/assets/javascripts/editor/submissions.js

@@ -204,7 +204,7 @@ CodeOceanEditorSubmissions = {
     this.teardownEventHandlers();
     this.createSubmission(button, null, function (response) {
       if (response.redirect) {
-        App.synchronized_editor?.unsubscribe();
+        App.synchronized_editor?.disconnect();
         this.autosaveIfChanged();
         this.stopCode(event);
         this.editors = [];