1 files changed, 58 insertions, 135 deletions
diff --git a/app/assets/javascripts/files_comment_button.js b/app/assets/javascripts/files_comment_button.js
index 534e651b030..d02e4cd5876 100644
--- a/app/assets/javascripts/files_comment_button.js
+++ b/app/assets/javascripts/files_comment_button.js
@@ -1,150 +1,73 @@
 /* eslint-disable func-names, space-before-function-paren, no-var, prefer-rest-params, wrap-iife, max-len, one-var, one-var-declaration-per-line, quotes, prefer-template, newline-per-chained-call, comma-dangle, new-cap, no-else-return, consistent-return */
-/* global FilesCommentButton */
 /* global notes */
 
-let $commentButtonTemplate;
-
-window.FilesCommentButton = (function() {
-  var COMMENT_BUTTON_CLASS, EMPTY_CELL_CLASS, LINE_COLUMN_CLASSES, LINE_CONTENT_CLASS, LINE_HOLDER_CLASS, LINE_NUMBER_CLASS, OLD_LINE_CLASS, TEXT_FILE_SELECTOR, UNFOLDABLE_LINE_CLASS;
-
-  COMMENT_BUTTON_CLASS = '.add-diff-note';
-
-  LINE_HOLDER_CLASS = '.line_holder';
-
-  LINE_NUMBER_CLASS = 'diff-line-num';
-
-  LINE_CONTENT_CLASS = 'line_content';
-
-  UNFOLDABLE_LINE_CLASS = 'js-unfold';
-
-  EMPTY_CELL_CLASS = 'empty-cell';
-
-  OLD_LINE_CLASS = 'old_line';
-
-  LINE_COLUMN_CLASSES = "." + LINE_NUMBER_CLASS + ", .line_content";
-
-  TEXT_FILE_SELECTOR = '.text-file';
-
-  function FilesCommentButton(filesContainerElement) {
-    this.render = this.render.bind(this);
-    this.hideButton = this.hideButton.bind(this);
-    this.isParallelView = notes.isParallelView();
-    filesContainerElement.on('mouseover', LINE_COLUMN_CLASSES, this.render)
-      .on('mouseleave', LINE_COLUMN_CLASSES, this.hideButton);
-  }
-
-  FilesCommentButton.prototype.render = function(e) {
-    var $currentTarget, buttonParentElement, lineContentElement, textFileElement, $button;
-    $currentTarget = $(e.currentTarget);
-
-    if ($currentTarget.hasClass('js-no-comment-btn')) return;
-
-    lineContentElement = this.getLineContent($currentTarget);
-    buttonParentElement = this.getButtonParent($currentTarget);
-
-    if (!this.validateButtonParent(buttonParentElement) || !this.validateLineContent(lineContentElement)) return;
-
-    $button = $(COMMENT_BUTTON_CLASS, buttonParentElement);
-    buttonParentElement.addClass('is-over')
-      .nextUntil(`.${LINE_CONTENT_CLASS}`).addClass('is-over');
-
-    if ($button.length) {
-      return;
+/* Developer beware! Do not add logic to showButton or hideButton
+ * that will force a reflow. Doing so will create a signficant performance
+ * bottleneck for pages with large diffs. For a comprehensive list of what
+ * causes reflows, visit https://gist.github.com/paulirish/5d52fb081b3570c81e3a
+ */
+
+const LINE_NUMBER_CLASS = 'diff-line-num';
+const UNFOLDABLE_LINE_CLASS = 'js-unfold';
+const NO_COMMENT_CLASS = 'no-comment-btn';
+const EMPTY_CELL_CLASS = 'empty-cell';
+const OLD_LINE_CLASS = 'old_line';
+const LINE_COLUMN_CLASSES = `.${LINE_NUMBER_CLASS}, .line_content`;
+const DIFF_CONTAINER_SELECTOR = '.files';
+const DIFF_EXPANDED_CLASS = 'diff-expanded';
+
+export default {
+  init($diffFile) {
+    /* Caching is used only when the following members are *true*. This is because there are likely to be
+     * differently configured versions of diffs in the same session. However if these values are true, they
+     * will be true in all cases */
+
+    if (!this.userCanCreateNote) {
+      // data-can-create-note is an empty string when true, otherwise undefined
+      this.userCanCreateNote = $diffFile.closest(DIFF_CONTAINER_SELECTOR).data('can-create-note') === '';
     }
 
-    textFileElement = this.getTextFileElement($currentTarget);
-    buttonParentElement.append(this.buildButton({
-      discussionID: lineContentElement.attr('data-discussion-id'),
-      lineType: lineContentElement.attr('data-line-type'),
-
-      noteableType: textFileElement.attr('data-noteable-type'),
-      noteableID: textFileElement.attr('data-noteable-id'),
-      commitID: textFileElement.attr('data-commit-id'),
-      noteType: lineContentElement.attr('data-note-type'),
-
-      // LegacyDiffNote
-      lineCode: lineContentElement.attr('data-line-code'),
-
-      // DiffNote
-      position: lineContentElement.attr('data-position')
-    }));
-  };
-
-  FilesCommentButton.prototype.hideButton = function(e) {
-    var $currentTarget = $(e.currentTarget);
-    var buttonParentElement = this.getButtonParent($currentTarget);
-
-    buttonParentElement.removeClass('is-over')
-      .nextUntil(`.${LINE_CONTENT_CLASS}`).removeClass('is-over');
-  };
-
-  FilesCommentButton.prototype.buildButton = function(buttonAttributes) {
-    return $commentButtonTemplate.clone().attr({
-      'data-discussion-id': buttonAttributes.discussionID,
-      'data-line-type': buttonAttributes.lineType,
-
-      'data-noteable-type': buttonAttributes.noteableType,
-      'data-noteable-id': buttonAttributes.noteableID,
-      'data-commit-id': buttonAttributes.commitID,
-      'data-note-type': buttonAttributes.noteType,
-
-      // LegacyDiffNote
-      'data-line-code': buttonAttributes.lineCode,
-
-      // DiffNote
-      'data-position': buttonAttributes.position
-    });
-  };
-
-  FilesCommentButton.prototype.getTextFileElement = function(hoveredElement) {
-    return hoveredElement.closest(TEXT_FILE_SELECTOR);
-  };
-
-  FilesCommentButton.prototype.getLineContent = function(hoveredElement) {
-    if (hoveredElement.hasClass(LINE_CONTENT_CLASS)) {
-      return hoveredElement;
-    }
-    if (!this.isParallelView) {
-      return $(hoveredElement).closest(LINE_HOLDER_CLASS).find("." + LINE_CONTENT_CLASS);
-    } else {
-      return $(hoveredElement).next("." + LINE_CONTENT_CLASS);
+    if (typeof notes !== 'undefined' && !this.isParallelView) {
+      this.isParallelView = notes.isParallelView && notes.isParallelView();
     }
-  };
 
-  FilesCommentButton.prototype.getButtonParent = function(hoveredElement) {
-    if (!this.isParallelView) {
-      if (hoveredElement.hasClass(OLD_LINE_CLASS)) {
-        return hoveredElement;
-      }
-      return hoveredElement.parent().find("." + OLD_LINE_CLASS);
-    } else {
-      if (hoveredElement.hasClass(LINE_NUMBER_CLASS)) {
-        return hoveredElement;
-      }
-      return $(hoveredElement).prev("." + LINE_NUMBER_CLASS);
+    if (this.userCanCreateNote) {
+      $diffFile.on('mouseover', LINE_COLUMN_CLASSES, e => this.showButton(this.isParallelView, e))
+        .on('mouseleave', LINE_COLUMN_CLASSES, e => this.hideButton(this.isParallelView, e));
     }
-  };
+  },
 
-  FilesCommentButton.prototype.validateButtonParent = function(buttonParentElement) {
-    return !buttonParentElement.hasClass(EMPTY_CELL_CLASS) && !buttonParentElement.hasClass(UNFOLDABLE_LINE_CLASS);
-  };
+  showButton(isParallelView, e) {
+    const buttonParentElement = this.getButtonParent(e.currentTarget, isParallelView);
 
-  FilesCommentButton.prototype.validateLineContent = function(lineContentElement) {
-    return lineContentElement.attr('data-note-type') && lineContentElement.attr('data-note-type') !== '';
-  };
+    if (!this.validateButtonParent(buttonParentElement)) return;
 
-  return FilesCommentButton;
-})();
+    buttonParentElement.classList.add('is-over');
+    buttonParentElement.nextElementSibling.classList.add('is-over');
+  },
 
-$.fn.filesCommentButton = function() {
-  $commentButtonTemplate = $('<button name="button" type="submit" class="add-diff-note js-add-diff-note-button" title="Add a comment to this line"><i class="fa fa-comment-o"></i></button>');
+  hideButton(isParallelView, e) {
+    const buttonParentElement = this.getButtonParent(e.currentTarget, isParallelView);
 
-  if (!(this && (this.parent().data('can-create-note') != null))) {
-    return;
-  }
-  return this.each(function() {
-    if (!$.data(this, 'filesCommentButton')) {
-      return $.data(this, 'filesCommentButton', new FilesCommentButton($(this)));
+    buttonParentElement.classList.remove('is-over');
+    buttonParentElement.nextElementSibling.classList.remove('is-over');
+  },
+
+  getButtonParent(hoveredElement, isParallelView) {
+    if (isParallelView) {
+      if (!hoveredElement.classList.contains(LINE_NUMBER_CLASS)) {
+        return hoveredElement.previousElementSibling;
+      }
+    } else if (!hoveredElement.classList.contains(OLD_LINE_CLASS)) {
+      return hoveredElement.parentNode.querySelector(`.${OLD_LINE_CLASS}`);
     }
-  });
+    return hoveredElement;
+  },
+
+  validateButtonParent(buttonParentElement) {
+    return !buttonParentElement.classList.contains(EMPTY_CELL_CLASS) &&
+      !buttonParentElement.classList.contains(UNFOLDABLE_LINE_CLASS) &&
+      !buttonParentElement.classList.contains(NO_COMMENT_CLASS) &&
+      !buttonParentElement.parentNode.classList.contains(DIFF_EXPANDED_CLASS);
+  },
 };