Limit discussions.json requests to maximum 2 in one batch

app/assets/javascripts/notes/constants.js

@@ -22,6 +22,8 @@ export const TIME_DIFFERENCE_VALUE = 10;
 export const ASC = 'asc';
 export const DESC = 'desc';
 
+export const DISCUSSION_FETCH_TIMEOUT = 750;
+
 export const NOTEABLE_TYPE_MAPPING = {
   Issue: ISSUE_NOTEABLE_TYPE,
   MergeRequest: MERGE_REQUEST_NOTEABLE_TYPE,

app/assets/javascripts/notes/stores/actions.js

@@ -87,6 +87,7 @@ export const fetchDiscussions = ({ commit, dispatch }, { path, filter, persistFi
 
   return axios.get(path, config).then(({ data }) => {
     commit(types.SET_INITIAL_DISCUSSIONS, data);
+    commit(types.SET_FETCHING_DISCUSSIONS, false);
 
     dispatch('updateResolvableDiscussionsCounts');
   });
@@ -136,6 +137,23 @@ export const updateNote = ({ commit, dispatch }, { endpoint, note }) =>
 
 export const updateOrCreateNotes = ({ commit, state, getters, dispatch }, notes) => {
   const { notesById } = getters;
+  const debouncedFetchDiscussions = isFetching => {
+    if (!isFetching) {
+      commit(types.SET_FETCHING_DISCUSSIONS, true);
+      dispatch('fetchDiscussions', { path: state.notesData.discussionsPath });
+    } else {
+      if (isFetching !== true) {
+        clearTimeout(state.currentlyFetchingDiscussions);
+      }
+
+      commit(
+        types.SET_FETCHING_DISCUSSIONS,
+        setTimeout(() => {
+          dispatch('fetchDiscussions', { path: state.notesData.discussionsPath });
+        }, constants.DISCUSSION_FETCH_TIMEOUT),
+      );
+    }
+  };
 
   notes.forEach(note => {
     if (notesById[note.id]) {
@@ -146,7 +164,7 @@ export const updateOrCreateNotes = ({ commit, state, getters, dispatch }, notes)
       if (discussion) {
         commit(types.ADD_NEW_REPLY_TO_DISCUSSION, note);
       } else if (note.type === constants.DIFF_NOTE) {
-        dispatch('fetchDiscussions', { path: state.notesData.discussionsPath });
+        debouncedFetchDiscussions(state.currentlyFetchingDiscussions);
       } else {
         commit(types.ADD_NEW_NOTE, note);
       }

app/assets/javascripts/notes/stores/modules/index.js

@@ -12,6 +12,7 @@ export default () => ({
     lastFetchedAt: null,
     currentDiscussionId: null,
     batchSuggestionsInfo: [],
+    currentlyFetchingDiscussions: false,
     /**
      * selectedCommentPosition & selectedCommentPosition structures are the same as `position.line_range`:
      * {

app/assets/javascripts/notes/stores/mutation_types.js

@@ -36,6 +36,7 @@ export const SET_CURRENT_DISCUSSION_ID = 'SET_CURRENT_DISCUSSION_ID';
 export const SET_DISCUSSIONS_SORT = 'SET_DISCUSSIONS_SORT';
 export const SET_SELECTED_COMMENT_POSITION = 'SET_SELECTED_COMMENT_POSITION';
 export const SET_SELECTED_COMMENT_POSITION_HOVER = 'SET_SELECTED_COMMENT_POSITION_HOVER';
+export const SET_FETCHING_DISCUSSIONS = 'SET_FETCHING_DISCUSSIONS';
 
 // Issue
 export const CLOSE_ISSUE = 'CLOSE_ISSUE';

app/assets/javascripts/notes/stores/mutations.js

@@ -379,4 +379,7 @@ export default {
   [types.UPDATE_ASSIGNEES](state, assignees) {
     state.noteableData.assignees = assignees;
   },
+  [types.SET_FETCHING_DISCUSSIONS](state, value) {
+    state.currentlyFetchingDiscussions = value;
+  },
 };

spec/frontend/notes/stores/actions_spec.js

@@ -3,6 +3,7 @@ import AxiosMockAdapter from 'axios-mock-adapter';
 import Api from '~/api';
 import { deprecatedCreateFlash as Flash } from '~/flash';
 import * as actions from '~/notes/stores/actions';
+import mutations from '~/notes/stores/mutations';
 import * as mutationTypes from '~/notes/stores/mutation_types';
 import * as notesConstants from '~/notes/constants';
 import createStore from '~/notes/stores';
@@ -651,6 +652,26 @@ describe('Actions Notes Store', () => {
   });
 
   describe('updateOrCreateNotes', () => {
+    it('Prevents `fetchDiscussions` being called multiple times within time limit', () => {
+      jest.useFakeTimers();
+      const note = { id: 1234, type: notesConstants.DIFF_NOTE };
+      const getters = { notesById: {} };
+      state = { discussions: [note], notesData: { discussionsPath: '' } };
+      commit.mockImplementation((type, value) => {
+        if (type === mutationTypes.SET_FETCHING_DISCUSSIONS) {
+          mutations[type](state, value);
+        }
+      });
+
+      actions.updateOrCreateNotes({ commit, state, getters, dispatch }, [note]);
+      actions.updateOrCreateNotes({ commit, state, getters, dispatch }, [note]);
+
+      jest.runAllTimers();
+      actions.updateOrCreateNotes({ commit, state, getters, dispatch }, [note]);
+
+      expect(dispatch).toHaveBeenCalledTimes(2);
+    });
+
     it('Updates existing note', () => {
       const note = { id: 1234 };
       const getters = { notesById: { 1234: note } };