diff --git a/polygerrit-ui/app/elements/diff/gr-diff-comment/gr-diff-comment.js b/polygerrit-ui/app/elements/diff/gr-diff-comment/gr-diff-comment.js
index a7a2db3..f87c14a 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-comment/gr-diff-comment.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-comment/gr-diff-comment.js
@@ -14,7 +14,7 @@
 (function() {
   'use strict';
 
-  var STORAGE_DEBOUNCE_INTERVAL = 400;
+  const STORAGE_DEBOUNCE_INTERVAL = 400;
 
   Polymer({
     is: 'gr-diff-comment',
@@ -116,55 +116,55 @@
       '_calculateActionstoShow(showActions, isRobotComment)',
     ],
 
-    attached: function() {
+    attached() {
       if (this.editing) {
         this.collapsed = false;
       } else if (this.comment) {
         this.collapsed = this.comment.collapsed;
       }
-      this._getIsAdmin().then(function(isAdmin) {
+      this._getIsAdmin().then(isAdmin => {
         this._isAdmin = isAdmin;
-      }.bind(this));
+      });
     },
 
-    detached: function() {
+    detached() {
       this.cancelDebouncer('fire-update');
     },
 
-    _computeShowHideText: function(collapsed) {
+    _computeShowHideText(collapsed) {
       return collapsed ? '◀' : '▼';
     },
 
-    _calculateActionstoShow: function(showActions, isRobotComment) {
+    _calculateActionstoShow(showActions, isRobotComment) {
       this._showHumanActions = showActions && !isRobotComment;
       this._showRobotActions = showActions && isRobotComment;
     },
 
-    _isRobotComment: function(comment) {
+    _isRobotComment(comment) {
       this.isRobotComment = !!comment.robot_id;
     },
 
-    isOnParent: function() {
+    isOnParent() {
       return this.side === 'PARENT';
     },
 
-    _getIsAdmin: function() {
+    _getIsAdmin() {
       return this.$.restAPI.getIsAdmin();
     },
 
-    save: function() {
+    save() {
       this.comment.message = this._messageText;
 
       this.disabled = true;
 
       this._eraseDraftComment();
 
-      this._xhrPromise = this._saveDraft(this.comment).then(function(response) {
+      this._xhrPromise = this._saveDraft(this.comment).then(response => {
         this.disabled = false;
         if (!response.ok) { return response; }
 
-        return this.$.restAPI.getResponseObject(response).then(function(obj) {
-          var comment = obj;
+        return this.$.restAPI.getResponseObject(response).then(obj => {
+          const comment = obj;
           comment.__draft = true;
           // Maintain the ephemeral draft ID for identification by other
           // elements.
@@ -176,17 +176,18 @@
           this.editing = false;
           this._fireSave();
           return obj;
-        }.bind(this));
-      }.bind(this)).catch(function(err) {
+        });
+      }).catch(err => {
         this.disabled = false;
         throw err;
-      }.bind(this));
+      });
     },
 
-    _eraseDraftComment: function() {
+    _eraseDraftComment() {
       // Prevents a race condition in which removing the draft comment occurs
       // prior to it being saved.
       this.cancelDebouncer('store');
+
       this.$.storage.eraseDraftComment({
         changeNum: this.changeNum,
         patchNum: this._getPatchNum(),
@@ -196,7 +197,7 @@
       });
     },
 
-    _commentChanged: function(comment) {
+    _commentChanged(comment) {
       this.editing = !!comment.__editing;
       this.resolved = !comment.unresolved;
       if (this.editing) { // It's a new draft/reply, notify.
@@ -204,41 +205,37 @@
       }
     },
 
-    _getEventPayload: function(opt_mixin) {
-      var payload = {
+    _getEventPayload(opt_mixin) {
+      return Object.assign({}, opt_mixin, {
         comment: this.comment,
         patchNum: this.patchNum,
-      };
-      for (var k in opt_mixin) {
-        payload[k] = opt_mixin[k];
-      }
-      return payload;
+      });
     },
 
-    _fireSave: function() {
+    _fireSave() {
       this.fire('comment-save', this._getEventPayload());
     },
 
-    _fireUpdate: function() {
-      this.debounce('fire-update', function() {
+    _fireUpdate() {
+      this.debounce('fire-update', () => {
         this.fire('comment-update', this._getEventPayload());
       });
     },
 
-    _draftChanged: function(draft) {
+    _draftChanged(draft) {
       this.$.container.classList.toggle('draft', draft);
     },
 
-    _editingChanged: function(editing, previousValue) {
+    _editingChanged(editing, previousValue) {
       this.$.container.classList.toggle('editing', editing);
       if (editing) {
-        var textarea = this.$.editTextarea.textarea;
+        const textarea = this.$.editTextarea.textarea;
         // Put the cursor at the end always.
         textarea.selectionStart = textarea.value.length;
         textarea.selectionEnd = textarea.selectionStart;
-        this.async(function() {
+        this.async(() => {
           textarea.focus();
-        }.bind(this));
+        });
       }
       if (this.comment && this.comment.id) {
         this.$$('.cancel').hidden = !editing;
@@ -252,15 +249,15 @@
       }
     },
 
-    _computeLinkToComment: function(comment) {
+    _computeLinkToComment(comment) {
       return '#' + comment.line;
     },
 
-    _computeSaveDisabled: function(draft) {
+    _computeSaveDisabled(draft) {
       return draft == null || draft.trim() == '';
     },
 
-    _handleTextareaKeydown: function(e) {
+    _handleTextareaKeydown(e) {
       switch (e.keyCode) {
         case 13: // 'enter'
           if (this._messageText.length !== 0 && (e.metaKey || e.ctrlKey)) {
@@ -280,11 +277,11 @@
       }
     },
 
-    _handleToggleCollapsed: function() {
+    _handleToggleCollapsed() {
       this.collapsed = !this.collapsed;
     },
 
-    _toggleCollapseClass: function(collapsed) {
+    _toggleCollapseClass(collapsed) {
       if (collapsed) {
         this.$.container.classList.add('collapsed');
       } else {
@@ -292,20 +289,20 @@
       }
     },
 
-    _commentMessageChanged: function(message) {
+    _commentMessageChanged(message) {
       this._messageText = message || '';
     },
 
-    _messageTextChanged: function(newValue, oldValue) {
+    _messageTextChanged(newValue, oldValue) {
       if (!this.comment || (this.comment && this.comment.id)) { return; }
 
       // Keep comment.message in sync so that gr-diff-comment-thread is aware
       // of the current message in the case that another comment is deleted.
       this.comment.message = this._messageText || '';
-      this.debounce('store', function() {
-        var message = this._messageText;
+      this.debounce('store', () => {
+        const message = this._messageText;
 
-        var commentLocation = {
+        const commentLocation = {
           changeNum: this.changeNum,
           patchNum: this._getPatchNum(),
           path: this.comment.path,
@@ -324,9 +321,9 @@
       }, STORAGE_DEBOUNCE_INTERVAL);
     },
 
-    _handleLinkTap: function(e) {
+    _handleLinkTap(e) {
       e.preventDefault();
-      var hash = this._computeLinkToComment(this.comment);
+      const hash = this._computeLinkToComment(this.comment);
       // Don't add the hash to the window history if it's already there.
       // Otherwise you mess up expected back button behavior.
       if (window.location.hash == hash) { return; }
@@ -335,52 +332,51 @@
       page.show(window.location.pathname + hash, null, false);
     },
 
-    _handleReply: function(e) {
+    _handleReply(e) {
       e.preventDefault();
       this.fire('create-reply-comment', this._getEventPayload(),
           {bubbles: false});
     },
 
-    _handleQuote: function(e) {
+    _handleQuote(e) {
       e.preventDefault();
       this.fire('create-reply-comment', this._getEventPayload({quote: true}),
           {bubbles: false});
     },
 
-    _handleFix: function(e) {
+    _handleFix(e) {
       e.preventDefault();
       this.fire('create-fix-comment', this._getEventPayload({quote: true}),
           {bubbles: false});
     },
 
-    _handleAck: function(e) {
+    _handleAck(e) {
       e.preventDefault();
       this.fire('create-ack-comment', this._getEventPayload(),
           {bubbles: false});
     },
 
-    _handleDone: function(e) {
+    _handleDone(e) {
       e.preventDefault();
       this.fire('create-done-comment', this._getEventPayload(),
           {bubbles: false});
     },
 
-    _handleEdit: function(e) {
+    _handleEdit(e) {
       e.preventDefault();
       this._messageText = this.comment.message;
       this.editing = true;
     },
 
-    _handleSave: function(e) {
+    _handleSave(e) {
       e.preventDefault();
       this.set('comment.__editing', false);
       this.save();
     },
 
-    _handleCancel: function(e) {
+    _handleCancel(e) {
       e.preventDefault();
-      if (!this.comment.message ||
-          this.comment.message.trim().length === 0) {
+      if (!this.comment.message || this.comment.message.trim().length === 0) {
         this._fireDiscard();
         return;
       }
@@ -388,12 +384,12 @@
       this.editing = false;
     },
 
-    _fireDiscard: function() {
+    _fireDiscard() {
       this.cancelDebouncer('fire-update');
       this.fire('comment-discard', this._getEventPayload());
     },
 
-    _handleDiscard: function(e) {
+    _handleDiscard(e) {
       e.preventDefault();
       if (!this.comment.__draft) {
         throw Error('Cannot discard a non-draft comment.');
@@ -408,32 +404,31 @@
         return;
       }
 
-      this._xhrPromise = this._deleteDraft(this.comment).then(
-          function(response) {
-            this.disabled = false;
-            if (!response.ok) { return response; }
+      this._xhrPromise = this._deleteDraft(this.comment).then(response => {
+        this.disabled = false;
+        if (!response.ok) { return response; }
 
-            this._fireDiscard();
-          }.bind(this)).catch(function(err) {
-            this.disabled = false;
-            throw err;
-          }.bind(this));
+        this._fireDiscard();
+      }).catch(err => {
+        this.disabled = false;
+        throw err;
+      });
     },
 
-    _saveDraft: function(draft) {
+    _saveDraft(draft) {
       return this.$.restAPI.saveDiffDraft(this.changeNum, this.patchNum, draft);
     },
 
-    _deleteDraft: function(draft) {
+    _deleteDraft(draft) {
       return this.$.restAPI.deleteDiffDraft(this.changeNum, this.patchNum,
           draft);
     },
 
-    _getPatchNum: function() {
+    _getPatchNum() {
       return this.isOnParent() ? 'PARENT' : this.patchNum;
     },
 
-    _loadLocalDraft: function(changeNum, patchNum, comment) {
+    _loadLocalDraft(changeNum, patchNum, comment) {
       // Only apply local drafts to comments that haven't been saved
       // remotely, and haven't been given a default message already.
       //
@@ -444,8 +439,8 @@
         return;
       }
 
-      var draft = this.$.storage.getDraftComment({
-        changeNum: changeNum,
+      const draft = this.$.storage.getDraftComment({
+        changeNum,
         patchNum: this._getPatchNum(),
         path: comment.path,
         line: comment.line,
@@ -457,40 +452,40 @@
       }
     },
 
-    _handleMouseEnter: function(e) {
+    _handleMouseEnter(e) {
       this.fire('comment-mouse-over', this._getEventPayload());
     },
 
-    _handleMouseLeave: function(e) {
+    _handleMouseLeave(e) {
       this.fire('comment-mouse-out', this._getEventPayload());
     },
 
-    _handleToggleResolved: function() {
+    _handleToggleResolved() {
       this.resolved = !this.resolved;
     },
 
-    _toggleResolved: function(resolved) {
+    _toggleResolved(resolved) {
       this.comment.unresolved = !resolved;
       this.fire('comment-update', this._getEventPayload());
     },
 
-    _handleCommentDelete: function() {
+    _handleCommentDelete() {
       Polymer.dom(Gerrit.getRootElement()).appendChild(this.$.overlay);
       this.$.overlay.open();
     },
 
-    _handleCancelDeleteComment: function() {
+    _handleCancelDeleteComment() {
       Polymer.dom(Gerrit.getRootElement()).removeChild(this.$.overlay);
       this.$.overlay.close();
     },
 
-    _handleConfirmDeleteComment: function() {
+    _handleConfirmDeleteComment() {
       this.$.restAPI.deleteComment(
           this.changeNum, this.patchNum, this.comment.id,
-        this.$.confirmDeleteComment.message).then(function(newComment) {
-          this._handleCancelDeleteComment();
-          this.comment = newComment;
-        }.bind(this));
+          this.$.confirmDeleteComment.message).then(newComment => {
+            this._handleCancelDeleteComment();
+            this.comment = newComment;
+          });
     },
   });
 })();
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-comment/gr-diff-comment_test.html b/polygerrit-ui/app/elements/diff/gr-diff-comment/gr-diff-comment_test.html
index ba6580a..835ecb8 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-comment/gr-diff-comment_test.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff-comment/gr-diff-comment_test.html
@@ -47,12 +47,12 @@
     return getComputedStyle(el).getPropertyValue('display') !== 'none';
   }
 
-  suite('gr-diff-comment tests', function() {
-    var element;
-    var sandbox;
-    setup(function() {
+  suite('gr-diff-comment tests', () => {
+    let element;
+    let sandbox;
+    setup(() => {
       stub('gr-rest-api-interface', {
-        getAccount: function() { return Promise.resolve(null); },
+        getAccount() { return Promise.resolve(null); },
       });
       element = fixture('basic');
       element.comment = {
@@ -68,11 +68,11 @@
       sandbox = sinon.sandbox.create();
     });
 
-    teardown(function() {
+    teardown(() => {
       sandbox.restore();
     });
 
-    test('collapsible comments', function() {
+    test('collapsible comments', () => {
       // When a comment (not draft) is loaded, it should be collapsed
       assert.isTrue(element.collapsed);
       assert.isFalse(isVisible(element.$$('gr-formatted-text')),
@@ -100,21 +100,20 @@
           'header middle content is not visible');
     });
 
-    test('clicking on date link does not trigger nav', function() {
-      var showStub = sinon.stub(page, 'show');
-      var dateEl = element.$$('.date');
+    test('clicking on date link does not trigger nav', () => {
+      const showStub = sinon.stub(page, 'show');
+      const dateEl = element.$$('.date');
       assert.ok(dateEl);
       MockInteractions.tap(dateEl);
-      var dest = window.location.pathname + '#5';
+      const dest = window.location.pathname + '#5';
       assert(showStub.lastCall.calledWithExactly(dest, null, false),
           'Should navigate to ' + dest + ' without triggering nav');
       showStub.restore();
     });
 
-    test('message is not retrieved from storage when other editing is true',
-        function(done) {
-      var storageStub = sandbox.stub(element.$.storage, 'getDraftComment');
-      var loadSpy = sandbox.spy(element, '_loadLocalDraft');
+    test('message is not retrieved from storage when other edits', done => {
+      const storageStub = sandbox.stub(element.$.storage, 'getDraftComment');
+      const loadSpy = sandbox.spy(element, '_loadLocalDraft');
 
       element.changeNum = 1;
       element.patchNum = 1;
@@ -126,17 +125,16 @@
         line: 5,
         __otherEditing: true,
       };
-      flush(function() {
+      flush(() => {
         assert.isTrue(loadSpy.called);
         assert.isFalse(storageStub.called);
         done();
       });
     });
 
-    test('message is retrieved from storage when there is no other editing',
-        function(done) {
-      var storageStub = sandbox.stub(element.$.storage, 'getDraftComment');
-      var loadSpy = sandbox.spy(element, '_loadLocalDraft');
+    test('message is retrieved from storage when no other edits', done => {
+      const storageStub = sandbox.stub(element.$.storage, 'getDraftComment');
+      const loadSpy = sandbox.spy(element, '_loadLocalDraft');
 
       element.changeNum = 1;
       element.patchNum = 1;
@@ -147,14 +145,14 @@
         },
         line: 5,
       };
-      flush(function() {
+      flush(() => {
         assert.isTrue(loadSpy.called);
         assert.isTrue(storageStub.called);
         done();
       });
     });
 
-    test('_getPatchNum', function() {
+    test('_getPatchNum', () => {
       element.side = 'PARENT';
       element.patchNum = 1;
       assert.equal(element._getPatchNum(), 'PARENT');
@@ -162,7 +160,7 @@
       assert.equal(element._getPatchNum(), 1);
     });
 
-    test('comment expand and collapse', function() {
+    test('comment expand and collapse', () => {
       element.collapsed = true;
       assert.isFalse(isVisible(element.$$('gr-formatted-text')),
           'gr-formatted-text is not visible');
@@ -185,8 +183,8 @@
           'header middle content is is not visible');
     });
 
-    suite('while editing', function() {
-      setup(function() {
+    suite('while editing', () => {
+      setup(() => {
         element.editing = true;
         element._messageText = 'test';
         sandbox.stub(element, '_handleCancel');
@@ -194,55 +192,55 @@
         flushAsynchronousOperations();
       });
 
-      suite('when text is empty', function() {
-        setup(function() {
+      suite('when text is empty', () => {
+        setup(() => {
           element._messageText = '';
         });
 
-        test('esc closes comment when text is empty', function() {
+        test('esc closes comment when text is empty', () => {
           MockInteractions.pressAndReleaseKeyOn(
               element.$.editTextarea, 27); // esc
           assert.isTrue(element._handleCancel.called);
         });
 
-        test('ctrl+enter does not save', function() {
+        test('ctrl+enter does not save', () => {
           MockInteractions.pressAndReleaseKeyOn(
               element.$.editTextarea, 13, 'ctrl'); // ctrl + enter
           assert.isFalse(element._handleSave.called);
         });
 
-        test('meta+enter does not save', function() {
+        test('meta+enter does not save', () => {
           MockInteractions.pressAndReleaseKeyOn(
               element.$.editTextarea, 13, 'meta'); // meta + enter
           assert.isFalse(element._handleSave.called);
         });
 
-        test('ctrl+s does not save', function() {
+        test('ctrl+s does not save', () => {
           MockInteractions.pressAndReleaseKeyOn(
               element.$.editTextarea, 83, 'ctrl'); // ctrl + s
           assert.isFalse(element._handleSave.called);
         });
       });
 
-      test('esc does not close comment that has content', function() {
+      test('esc does not close comment that has content', () => {
         MockInteractions.pressAndReleaseKeyOn(
             element.$.editTextarea, 27); // esc
         assert.isFalse(element._handleCancel.called);
       });
 
-      test('ctrl+enter saves', function() {
+      test('ctrl+enter saves', () => {
         MockInteractions.pressAndReleaseKeyOn(
             element.$.editTextarea, 13, 'ctrl'); // ctrl + enter
         assert.isTrue(element._handleSave.called);
       });
 
-      test('meta+enter saves', function() {
+      test('meta+enter saves', () => {
         MockInteractions.pressAndReleaseKeyOn(
             element.$.editTextarea, 13, 'meta'); // meta + enter
         assert.isTrue(element._handleSave.called);
       });
 
-      test('ctrl+s saves', function() {
+      test('ctrl+s saves', () => {
         MockInteractions.pressAndReleaseKeyOn(
             element.$.editTextarea, 83, 'ctrl'); // ctrl + s
         assert.isTrue(element._handleSave.called);
@@ -271,19 +269,19 @@
     });
   });
 
-  suite('gr-diff-comment draft tests', function() {
-    var element;
-    var sandbox;
+  suite('gr-diff-comment draft tests', () => {
+    let element;
+    let sandbox;
 
-    setup(function() {
+    setup(() => {
       stub('gr-rest-api-interface', {
-        getAccount: function() { return Promise.resolve(null); },
-        saveDiffDraft: function() {
+        getAccount() { return Promise.resolve(null); },
+        saveDiffDraft() {
           return Promise.resolve({
             ok: true,
-            text: function() {
+            text() {
               return Promise.resolve(
-                ')]}\'\n{' +
+                  ')]}\'\n{' +
                   '"id": "baf0414d_40572e03",' +
                   '"path": "/path/to/file",' +
                   '"line": 5,' +
@@ -294,12 +292,12 @@
             },
           });
         },
-        removeChangeReviewer: function() {
+        removeChangeReviewer() {
           return Promise.resolve({ok: true});
         },
       });
       stub('gr-storage', {
-        getDraftComment: function() { return null; },
+        getDraftComment() { return null; },
       });
       element = fixture('draft');
       element.changeNum = 42;
@@ -316,11 +314,11 @@
       sandbox = sinon.sandbox.create();
     });
 
-    teardown(function() {
+    teardown(() => {
       sandbox.restore();
     });
 
-    test('button visibility states', function() {
+    test('button visibility states', () => {
       element.showActions = false;
       assert.isTrue(element.$$('.humanActions').hasAttribute('hidden'));
       assert.isTrue(element.$$('.robotActions').hasAttribute('hidden'));
@@ -377,7 +375,7 @@
       assert.isFalse(element.$$('.robotActions').hasAttribute('hidden'));
     });
 
-    test('collapsible drafts', function() {
+    test('collapsible drafts', () => {
       assert.isTrue(element.collapsed);
       assert.isFalse(isVisible(element.$$('gr-formatted-text')),
           'gr-formatted-text is not visible');
@@ -438,26 +436,26 @@
           'header middle content is not visible');
     });
 
-    test('draft creation/cancelation', function(done) {
+    test('draft creation/cancelation', done => {
       assert.isFalse(element.editing);
       MockInteractions.tap(element.$$('.edit'));
       assert.isTrue(element.editing);
 
       element._messageText = '';
-      var eraseMessageDraftSpy = sandbox.spy(element, '_eraseDraftComment');
+      const eraseMessageDraftSpy = sandbox.spy(element, '_eraseDraftComment');
 
       // Save should be disabled on an empty message.
-      var disabled = element.$$('.save').hasAttribute('disabled');
+      let disabled = element.$$('.save').hasAttribute('disabled');
       assert.isTrue(disabled, 'save button should be disabled.');
       element._messageText = '     ';
       disabled = element.$$('.save').hasAttribute('disabled');
       assert.isTrue(disabled, 'save button should be disabled.');
 
-      var updateStub = sinon.stub();
+      const updateStub = sinon.stub();
       element.addEventListener('comment-update', updateStub);
 
-      var numDiscardEvents = 0;
-      element.addEventListener('comment-discard', function(e) {
+      let numDiscardEvents = 0;
+      element.addEventListener('comment-discard', e => {
         numDiscardEvents++;
         assert.isFalse(eraseMessageDraftSpy.called);
         if (numDiscardEvents === 2) {
@@ -471,32 +469,31 @@
       MockInteractions.pressAndReleaseKeyOn(element.$.editTextarea, 27); // esc
     });
 
-    test('draft discard removes message from storage', function(done) {
+    test('draft discard removes message from storage', done => {
       element._messageText = '';
-      var eraseMessageDraftSpy = sandbox.spy(element, '_eraseDraftComment');
+      const eraseMessageDraftSpy = sandbox.spy(element, '_eraseDraftComment');
 
-      var numDiscardEvents = 0;
-      element.addEventListener('comment-discard', function(e) {
+      element.addEventListener('comment-discard', e => {
         assert.isTrue(eraseMessageDraftSpy.called);
         done();
       });
       MockInteractions.tap(element.$$('.discard'));
     });
 
-    test('ctrl+s saves comment', function(done) {
-      var stub = sinon.stub(element, 'save', function() {
+    test('ctrl+s saves comment', done => {
+      const stub = sinon.stub(element, 'save', () => {
         assert.isTrue(stub.called);
         stub.restore();
         done();
       });
       element._messageText = 'is that the horse from horsing around??';
       MockInteractions.pressAndReleaseKeyOn(
-        element.$.editTextarea.textarea,
-        83, 'ctrl');  // 'ctrl + s'
+          element.$.editTextarea.textarea,
+          83, 'ctrl');  // 'ctrl + s'
     });
 
-    test('draft saving/editing', function(done) {
-      var fireStub = sinon.stub(element, 'fire');
+    test('draft saving/editing', done => {
+      const fireStub = sinon.stub(element, 'fire');
       let cancelDebounce = sandbox.stub(element, 'cancelDebouncer');
 
       element.draft = true;
@@ -505,7 +502,7 @@
       element.flushDebouncer('fire-update');
       element.flushDebouncer('store');
       assert(fireStub.calledWith('comment-update'),
-             'comment-update should be sent');
+          'comment-update should be sent');
       assert.deepEqual(fireStub.lastCall.args, [
         'comment-update', {
           comment: {
@@ -526,10 +523,11 @@
       assert.isTrue(element.disabled,
           'Element should be disabled when creating draft.');
 
-      element._xhrPromise.then(function(draft) {
+      element._xhrPromise.then(draft => {
         assert(fireStub.calledWith('comment-save'),
-               'comment-save should be sent');
+            'comment-save should be sent');
         assert(cancelDebounce.calledWith('store'));
+
         assert.deepEqual(fireStub.lastCall.args[1], {
           comment: {
             __commentSide: 'right',
@@ -545,10 +543,10 @@
           patchNum: 1,
         });
         assert.isFalse(element.disabled,
-                       'Element should be enabled when done creating draft.');
+            'Element should be enabled when done creating draft.');
         assert.equal(draft.message, 'saved!');
         assert.isFalse(element.editing);
-      }).then(function() {
+      }).then(() => {
         MockInteractions.tap(element.$$('.edit'));
         element._messageText = 'You’ll be delivering a package to Chapek 9, ' +
             'a world where humans are killed on sight.';
@@ -556,7 +554,7 @@
         assert.isTrue(element.disabled,
             'Element should be disabled when updating draft.');
 
-        element._xhrPromise.then(function(draft) {
+        element._xhrPromise.then(draft => {
           assert.isFalse(element.disabled,
               'Element should be enabled when done updating draft.');
           assert.equal(draft.message, 'saved!');
@@ -567,26 +565,26 @@
       });
     });
 
-    test('clicking on date link does not trigger nav', function() {
-      var showStub = sinon.stub(page, 'show');
-      var dateEl = element.$$('.date');
+    test('clicking on date link does not trigger nav', () => {
+      const showStub = sinon.stub(page, 'show');
+      const dateEl = element.$$('.date');
       assert.ok(dateEl);
       MockInteractions.tap(dateEl);
-      var dest = window.location.pathname + '#5';
+      const dest = window.location.pathname + '#5';
       assert(showStub.lastCall.calledWithExactly(dest, null, false),
           'Should navigate to ' + dest + ' without triggering nav');
       showStub.restore();
     });
 
-    test('proper event fires on resolve', function(done) {
-      element.addEventListener('comment-update', function(e) {
+    test('proper event fires on resolve', done => {
+      element.addEventListener('comment-update', e => {
         assert.isTrue(e.detail.comment.unresolved);
         done();
       });
       MockInteractions.tap(element.$$('.resolve input'));
     });
 
-    test('resolved comment state indicated by checkbox', function() {
+    test('resolved comment state indicated by checkbox', () => {
       element.comment = {unresolved: false};
       assert.isTrue(element.$$('.resolve input').checked);
       element.comment = {unresolved: true};