Add disposeAutoSave method autosave mixin.

app/assets/javascripts/notes/components/noteable_discussion.vue

@@ -152,7 +152,7 @@ export default {
           this.initAutoSave(this.transformedDiscussion, ['Reply']);
         });
       } else {
-        this.autosave.dispose();
+        this.disposeAutoSave();
       }
     },
   },

app/assets/javascripts/notes/mixins/autosave.js

@@ -23,5 +23,8 @@ export default {
     setAutoSave() {
       this.autosave.save();
     },
+    disposeAutoSave() {
+      this.autosave.dispose();
+    },
   },
 };