Merge branch 'discussion-reply-button-performance' into 'master'

Remove delay when hitting Reply... button on page with a lot of comments

Every time the "Reply..." button was hit, a new `GLForm` was instantiated (which is fine), which would then call `GitLab.GfmAutoComplete.setup()` without specifying which textarea we needed autocompletion on, which resulted in `GitLab.GfmAutoComplete.setup` iterating through every single textarea on the page. On a page with a lot of comments, where each comment would have its own textarea that will be used to edit the comment, this would take a long time and cause the whole page to hang for 2 seconds when a  "Reply..." button was clicked.

See merge request !5602

3 files changed, 4 insertions, 3 deletions

diff --git a/CHANGELOG b/CHANGELOG
index b936d91aa14..db2617dcbd7 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -19,6 +19,7 @@ v 8.11.0 (unreleased)
   - Clean up unused routes (Josef Strzibny)
   - Add green outline to New Branch button. !5447 (winniehell)
   - Update to gitlab_git 10.4.1 and take advantage of preserved Ref objects
+  - Remove delay when hitting "Reply..." button on page with a lot of discussions
   - Retrieve rendered HTML from cache in one request
   - Fix renaming repository when name contains invalid chararacters under project settings
   - Optimize checking if a user has read access to a list of issues !5370
diff --git a/app/assets/javascripts/gfm_auto_complete.js b/app/assets/javascripts/gfm_auto_complete.js
index 41f4c1914f2..2e5b15f4b77 100644
--- a/app/assets/javascripts/gfm_auto_complete.js
+++ b/app/assets/javascripts/gfm_auto_complete.js
@@ -47,8 +47,8 @@
         }
       }
     },
-    setup: function(wrap) {
-      this.input = $('.js-gfm-input');
+    setup: function(input) {
+      this.input = input || $('.js-gfm-input');
       this.destroyAtWho();
       this.setupAtWho();
       if (this.dataSource) {
diff --git a/app/assets/javascripts/gl_form.js b/app/assets/javascripts/gl_form.js
index 6ac7564a848..528a673eb15 100644
--- a/app/assets/javascripts/gl_form.js
+++ b/app/assets/javascripts/gl_form.js
@@ -21,7 +21,7 @@
         this.form.find('.div-dropzone').remove();
         this.form.addClass('gfm-form');
         disableButtonIfEmptyField(this.form.find('.js-note-text'), this.form.find('.js-comment-button'));
-        GitLab.GfmAutoComplete.setup();
+        GitLab.GfmAutoComplete.setup(this.form.find('.js-gfm-input'));
         new DropzoneInput(this.form);
         autosize(this.textarea);
         this.addEventListeners();