diff --git a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js
index f0f814f580..e8855d769c 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js
@@ -14,17 +14,17 @@
 (function() {
   'use strict';
 
-  var COMMIT_MESSAGE_PATH = '/COMMIT_MSG';
-  var MERGE_LIST_PATH = '/MERGE_LIST';
+  const COMMIT_MESSAGE_PATH = '/COMMIT_MSG';
+  const MERGE_LIST_PATH = '/MERGE_LIST';
 
-  var COMMENT_SAVE = 'Try again when all comments have saved.';
+  const COMMENT_SAVE = 'Try again when all comments have saved.';
 
-  var DiffSides = {
+  const DiffSides = {
     LEFT: 'left',
     RIGHT: 'right',
   };
 
-  var HASH_PATTERN = /^[ab]?\d+$/;
+  const HASH_PATTERN = /^[ab]?\d+$/;
 
   Polymer({
     is: 'gr-diff-view',
@@ -51,12 +51,12 @@
       },
       keyEventTarget: {
         type: Object,
-        value: function() { return document.body; },
+        value() { return document.body; },
       },
       changeViewState: {
         type: Object,
         notify: true,
-        value: function() { return {}; },
+        value() { return {}; },
       },
 
       _patchRange: Object,
@@ -65,7 +65,7 @@
       _diff: Object,
       _fileList: {
         type: Array,
-        value: function() { return []; },
+        value() { return []; },
       },
       _path: {
         type: String,
@@ -134,18 +134,18 @@
       ',': '_handleCommaKey',
     },
 
-    attached: function() {
-      this._getLoggedIn().then(function(loggedIn) {
+    attached() {
+      this._getLoggedIn().then(loggedIn => {
         this._loggedIn = loggedIn;
         if (loggedIn) {
           this._setReviewed(true);
         }
-      }.bind(this));
+      });
       if (this.changeViewState.diffMode === null) {
         // If screen size is small, always default to unified view.
-        this.$.restAPI.getPreferences().then(function(prefs) {
+        this.$.restAPI.getPreferences().then(prefs => {
           this.set('changeViewState.diffMode', prefs.default_diff_view);
-        }.bind(this));
+        });
       }
 
       if (this._path) {
@@ -156,63 +156,63 @@
       this.$.cursor.push('diffs', this.$.diff);
     },
 
-    _getLoggedIn: function() {
+    _getLoggedIn() {
       return this.$.restAPI.getLoggedIn();
     },
 
-    _getProjectConfig: function(project) {
+    _getProjectConfig(project) {
       return this.$.restAPI.getProjectConfig(project).then(
-          function(config) {
+          config => {
             this._projectConfig = config;
-          }.bind(this));
+          });
     },
 
-    _getChangeDetail: function(changeNum) {
+    _getChangeDetail(changeNum) {
       return this.$.restAPI.getDiffChangeDetail(changeNum).then(
-          function(change) {
+          change => {
             this._change = change;
-          }.bind(this));
+          });
     },
 
-    _getFiles: function(changeNum, patchRangeRecord) {
-      var patchRange = patchRangeRecord.base;
+    _getFiles(changeNum, patchRangeRecord) {
+      const patchRange = patchRangeRecord.base;
       return this.$.restAPI.getChangeFilePathsAsSpeciallySortedArray(
-          changeNum, patchRange).then(function(files) {
+          changeNum, patchRange).then(files => {
             this._fileList = files;
-          }.bind(this));
+          });
     },
 
-    _getDiffPreferences: function() {
+    _getDiffPreferences() {
       return this.$.restAPI.getDiffPreferences();
     },
 
-    _getPreferences: function() {
+    _getPreferences() {
       return this.$.restAPI.getPreferences();
     },
 
-    _getWindowWidth: function() {
+    _getWindowWidth() {
       return window.innerWidth;
     },
 
-    _handleReviewedChange: function(e) {
+    _handleReviewedChange(e) {
       this._setReviewed(Polymer.dom(e).rootTarget.checked);
     },
 
-    _setReviewed: function(reviewed) {
+    _setReviewed(reviewed) {
       this.$.reviewed.checked = reviewed;
-      this._saveReviewedState(reviewed).catch(function(err) {
+      this._saveReviewedState(reviewed).catch(err => {
         alert('Couldn’t change file review status. Check the console ' +
             'and contact the PolyGerrit team for assistance.');
         throw err;
-      }.bind(this));
+      });
     },
 
-    _saveReviewedState: function(reviewed) {
+    _saveReviewedState(reviewed) {
       return this.$.restAPI.saveFileReviewed(this._changeNum,
           this._patchRange.patchNum, this._path, reviewed);
     },
 
-    _handleEscKey: function(e) {
+    _handleEscKey(e) {
       if (this.shouldSuppressKeyboardShortcut(e) ||
           this.modifierPressed(e)) { return; }
 
@@ -220,21 +220,21 @@
       this.$.diff.displayLine = false;
     },
 
-    _handleShiftLeftKey: function(e) {
+    _handleShiftLeftKey(e) {
       if (this.shouldSuppressKeyboardShortcut(e)) { return; }
 
       e.preventDefault();
       this.$.cursor.moveLeft();
     },
 
-    _handleShiftRightKey: function(e) {
+    _handleShiftRightKey(e) {
       if (this.shouldSuppressKeyboardShortcut(e)) { return; }
 
       e.preventDefault();
       this.$.cursor.moveRight();
     },
 
-    _handleUpKey: function(e) {
+    _handleUpKey(e) {
       if (this.shouldSuppressKeyboardShortcut(e)) { return; }
       if (e.detail.keyboardEvent.shiftKey &&
           e.detail.keyboardEvent.keyCode === 75) { // 'K'
@@ -248,7 +248,7 @@
       this.$.cursor.moveUp();
     },
 
-    _handleDownKey: function(e) {
+    _handleDownKey(e) {
       if (this.shouldSuppressKeyboardShortcut(e)) { return; }
       if (e.detail.keyboardEvent.shiftKey &&
           e.detail.keyboardEvent.keyCode === 74) { // 'J'
@@ -262,33 +262,33 @@
       this.$.cursor.moveDown();
     },
 
-    _moveToPreviousFileWithComment: function() {
+    _moveToPreviousFileWithComment() {
       if (this._commentSkips && this._commentSkips.previous) {
         page.show(this._getDiffURL(this._changeNum, this._patchRange,
             this._commentSkips.previous));
       }
     },
 
-    _moveToNextFileWithComment: function() {
+    _moveToNextFileWithComment() {
       if (this._commentSkips && this._commentSkips.next) {
         page.show(this._getDiffURL(this._changeNum, this._patchRange,
             this._commentSkips.next));
       }
     },
 
-    _handleCKey: function(e) {
+    _handleCKey(e) {
       if (this.shouldSuppressKeyboardShortcut(e)) { return; }
       if (this.$.diff.isRangeSelected()) { return; }
       if (this.modifierPressed(e)) { return; }
 
       e.preventDefault();
-      var line = this.$.cursor.getTargetLineElement();
+      const line = this.$.cursor.getTargetLineElement();
       if (line) {
         this.$.diff.addDraftAtLine(line);
       }
     },
 
-    _handleLeftBracketKey: function(e) {
+    _handleLeftBracketKey(e) {
       if (this.shouldSuppressKeyboardShortcut(e) ||
           this.modifierPressed(e)) { return; }
 
@@ -296,7 +296,7 @@
       this._navToFile(this._path, this._fileList, -1);
     },
 
-    _handleRightBracketKey: function(e) {
+    _handleRightBracketKey(e) {
       if (this.shouldSuppressKeyboardShortcut(e) ||
           this.modifierPressed(e)) { return; }
 
@@ -304,7 +304,7 @@
       this._navToFile(this._path, this._fileList, 1);
     },
 
-    _handleNKey: function(e) {
+    _handleNKey(e) {
       if (this.shouldSuppressKeyboardShortcut(e)) { return; }
 
       e.preventDefault();
@@ -316,7 +316,7 @@
       }
     },
 
-    _handlePKey: function(e) {
+    _handlePKey(e) {
       if (this.shouldSuppressKeyboardShortcut(e)) { return; }
 
       e.preventDefault();
@@ -328,7 +328,7 @@
       }
     },
 
-    _handleAKey: function(e) {
+    _handleAKey(e) {
       if (this.shouldSuppressKeyboardShortcut(e)) { return; }
 
       if (e.detail.keyboardEvent.shiftKey) { // Hide left diff.
@@ -351,7 +351,7 @@
       this._navToChangeView();
     },
 
-    _handleUKey: function(e) {
+    _handleUKey(e) {
       if (this.shouldSuppressKeyboardShortcut(e) ||
           this.modifierPressed(e)) { return; }
 
@@ -359,7 +359,7 @@
       this._navToChangeView();
     },
 
-    _handleCommaKey: function(e) {
+    _handleCommaKey(e) {
       if (this.shouldSuppressKeyboardShortcut(e) ||
           this.modifierPressed(e)) { return; }
 
@@ -367,7 +367,7 @@
       this.$.diffPreferences.open();
     },
 
-    _navToChangeView: function() {
+    _navToChangeView() {
       if (!this._changeNum || !this._patchRange.patchNum) { return; }
 
       page.show(this._getChangePath(
@@ -376,15 +376,15 @@
           this._change && this._change.revisions));
     },
 
-    _computeUpURL: function(changeNum, patchRange, change, changeRevisions) {
+    _computeUpURL(changeNum, patchRange, change, changeRevisions) {
       return this._getChangePath(
           changeNum,
           patchRange,
           change && changeRevisions);
     },
 
-    _navToFile: function(path, fileList, direction) {
-      var url = this._computeNavLinkURL(path, fileList, direction);
+    _navToFile(path, fileList, direction) {
+      const url = this._computeNavLinkURL(path, fileList, direction);
       if (!url) { return; }
 
       page.show(this._computeNavLinkURL(path, fileList, direction));
@@ -401,12 +401,14 @@
      * @return {?string} The next URL when proceeding in the specified
      *     direction.
      */
-    _computeNavLinkURL: function(path, fileList, direction, opt_noUp) {
+    _computeNavLinkURL(path, fileList, direction, opt_noUp) {
       if (!path || fileList.length === 0) { return null; }
 
-      var idx = fileList.indexOf(path);
+      let idx = fileList.indexOf(path);
       if (idx === -1) {
-        var file = direction > 0 ? fileList[0] : fileList[fileList.length - 1];
+        const file = direction > 0 ?
+            fileList[0] :
+            fileList[fileList.length - 1];
         return this._getDiffURL(this._changeNum, this._patchRange, file);
       }
 
@@ -423,7 +425,7 @@
       return this._getDiffURL(this._changeNum, this._patchRange, fileList[idx]);
     },
 
-    _paramsChanged: function(value) {
+    _paramsChanged(value) {
       if (value.view != this.tagName.toLowerCase()) { return; }
 
       this._loadHash(location.hash);
@@ -445,33 +447,33 @@
         return;
       }
 
-      var promises = [];
+      const promises = [];
 
       this._localPrefs = this.$.storage.getPreferences();
-      promises.push(this._getDiffPreferences().then(function(prefs) {
+      promises.push(this._getDiffPreferences().then(prefs => {
         this._prefs = prefs;
-      }.bind(this)));
+      }));
 
-      promises.push(this._getPreferences().then(function(prefs) {
+      promises.push(this._getPreferences().then(prefs => {
         this._userPrefs = prefs;
-      }.bind(this)));
+      }));
 
       promises.push(this._getChangeDetail(this._changeNum));
 
-      Promise.all(promises).then(function() {
+      Promise.all(promises).then(() => {
         this._loading = false;
         this.$.diff.reload();
-      }.bind(this));
+      });
 
-      this._loadCommentMap().then(function(commentMap) {
+      this._loadCommentMap().then(commentMap => {
         this._commentMap = commentMap;
-      }.bind(this));
+      });
     },
 
     /**
      * If the URL hash is a diff address then configure the diff cursor.
      */
-    _loadHash: function(hash) {
+    _loadHash(hash) {
       hash = hash.replace(/^#/, '');
       if (!HASH_PATTERN.test(hash)) { return; }
       if (hash[0] === 'a' || hash[0] === 'b') {
@@ -483,7 +485,7 @@
       this.$.cursor.initialLineNumber = parseInt(hash, 10);
     },
 
-    _pathChanged: function(path) {
+    _pathChanged(path) {
       if (this._fileList.length == 0) { return; }
 
       this.set('changeViewState.selectedFileIndex',
@@ -494,17 +496,17 @@
       }
     },
 
-    _getDiffURL: function(changeNum, patchRange, path) {
+    _getDiffURL(changeNum, patchRange, path) {
       return this.getBaseUrl() + '/c/' + changeNum + '/' +
           this._patchRangeStr(patchRange) + '/' + this.encodeURL(path, true);
     },
 
-    _computeDiffURL: function(changeNum, patchRangeRecord, path) {
+    _computeDiffURL(changeNum, patchRangeRecord, path) {
       return this._getDiffURL(changeNum, patchRangeRecord.base, path);
     },
 
-    _patchRangeStr: function(patchRange) {
-      var patchStr = patchRange.patchNum;
+    _patchRangeStr(patchRange) {
+      let patchStr = patchRange.patchNum;
       if (patchRange.basePatchNum != null &&
           patchRange.basePatchNum != 'PARENT') {
         patchStr = patchRange.basePatchNum + '..' + patchRange.patchNum;
@@ -512,25 +514,25 @@
       return patchStr;
     },
 
-    _computeAvailablePatches: function(revisions) {
-      var patchNums = [];
-      for (var rev in revisions) {
-        patchNums.push(revisions[rev]._number);
+    _computeAvailablePatches(revisions) {
+      const patchNums = [];
+      for (const rev of Object.values(revisions)) {
+        patchNums.push(rev._number);
       }
-      return patchNums.sort(function(a, b) { return a - b; });
+      return patchNums.sort((a, b) => { return a - b; });
     },
 
-    _getChangePath: function(changeNum, patchRange, revisions) {
-      var base = this.getBaseUrl() + '/c/' + changeNum + '/';
+    _getChangePath(changeNum, patchRange, revisions) {
+      const base = this.getBaseUrl() + '/c/' + changeNum + '/';
 
       // The change may not have loaded yet, making revisions unavailable.
       if (!revisions) {
         return base + this._patchRangeStr(patchRange);
       }
 
-      var latestPatchNum = -1;
-      for (var rev in revisions) {
-        latestPatchNum = Math.max(latestPatchNum, revisions[rev]._number);
+      let latestPatchNum = -1;
+      for (const rev of Object.values(revisions)) {
+        latestPatchNum = Math.max(latestPatchNum, rev._number);
       }
       if (patchRange.basePatchNum !== 'PARENT' ||
           parseInt(patchRange.patchNum, 10) !== latestPatchNum) {
@@ -540,11 +542,11 @@
       return base;
     },
 
-    _computeChangePath: function(changeNum, patchRangeRecord, revisions) {
+    _computeChangePath(changeNum, patchRangeRecord, revisions) {
       return this._getChangePath(changeNum, patchRangeRecord.base, revisions);
     },
 
-    _computeFileDisplayName: function(path) {
+    _computeFileDisplayName(path) {
       if (path === COMMIT_MESSAGE_PATH) {
         return 'Commit message';
       } else if (path === MERGE_LIST_PATH) {
@@ -553,20 +555,20 @@
       return path;
     },
 
-    _computeTruncatedFileDisplayName: function(path) {
+    _computeTruncatedFileDisplayName(path) {
       return util.truncatePath(this._computeFileDisplayName(path));
     },
 
-    _computeFileSelected: function(path, currentPath) {
+    _computeFileSelected(path, currentPath) {
       return path == currentPath;
     },
 
-    _computePrefsButtonHidden: function(prefs, loggedIn) {
+    _computePrefsButtonHidden(prefs, loggedIn) {
       return !loggedIn || !prefs;
     },
 
-    _computeKeyNav: function(path, selectedPath, fileList) {
-      var selectedIndex = fileList.indexOf(selectedPath);
+    _computeKeyNav(path, selectedPath, fileList) {
+      const selectedIndex = fileList.indexOf(selectedPath);
       if (fileList.indexOf(path) == selectedIndex - 1) {
         return '[';
       }
@@ -576,41 +578,41 @@
       return '';
     },
 
-    _handleFileTap: function(e) {
+    _handleFileTap(e) {
       // async is needed so that that the click event is fired before the
       // dropdown closes (This was a bug for touch devices).
-      this.async(function() {
+      this.async(() => {
         this.$.dropdown.close();
       }, 1);
     },
 
-    _handleMobileSelectChange: function(e) {
-      var path = Polymer.dom(e).rootTarget.value;
+    _handleMobileSelectChange(e) {
+      const path = Polymer.dom(e).rootTarget.value;
       page.show(this._getDiffURL(this._changeNum, this._patchRange, path));
     },
 
-    _showDropdownTapHandler: function(e) {
+    _showDropdownTapHandler(e) {
       this.$.dropdown.open();
     },
 
-    _handlePrefsTap: function(e) {
+    _handlePrefsTap(e) {
       e.preventDefault();
       this.$.diffPreferences.open();
     },
 
-    _handlePrefsSave: function(e) {
+    _handlePrefsSave(e) {
       e.stopPropagation();
-      var el = Polymer.dom(e).rootTarget;
+      const el = Polymer.dom(e).rootTarget;
       el.disabled = true;
       this.$.storage.savePreferences(this._localPrefs);
-      this._saveDiffPreferences().then(function(response) {
+      this._saveDiffPreferences().then(response => {
         el.disabled = false;
         if (!response.ok) { return response; }
 
         this.$.prefsOverlay.close();
-      }.bind(this)).catch(function(err) {
+      }).catch(err => {
         el.disabled = false;
-      }.bind(this));
+      });
     },
 
     /**
@@ -627,7 +629,7 @@
      *
      * @return {String}
      */
-    _getDiffViewMode: function() {
+    _getDiffViewMode() {
       if (this.changeViewState.diffMode) {
         return this.changeViewState.diffMode;
       } else if (this._userPrefs) {
@@ -638,17 +640,17 @@
       }
     },
 
-    _computeModeSelectHidden: function() {
+    _computeModeSelectHidden() {
       return this._isImageDiff;
     },
 
-    _onLineSelected: function(e, detail) {
+    _onLineSelected(e, detail) {
       this.$.cursor.moveToLineNumber(detail.number, detail.side);
       history.replaceState(null, null, '#' + this.$.cursor.getAddress());
     },
 
-    _computeDownloadLink: function(changeNum, patchRange, path) {
-      var url = this.changeBaseURL(changeNum, patchRange.patchNum);
+    _computeDownloadLink(changeNum, patchRange, path) {
+      let url = this.changeBaseURL(changeNum, patchRange.patchNum);
       url += '/patch?zip&path=' + encodeURIComponent(path);
       return url;
     },
@@ -659,9 +661,9 @@
      * current patch range.
      * @return {Promise} A promise that yields a comment map object.
      */
-    _loadCommentMap: function() {
-      function filterByRange(comment) {
-        var patchNum = comment.patch_set + '';
+    _loadCommentMap() {
+      const filterByRange = comment => {
+        const patchNum = comment.patch_set + '';
         return patchNum === this._patchRange.patchNum ||
             patchNum === this._patchRange.basePatchNum;
       };
@@ -670,34 +672,34 @@
         this.$.restAPI.getDiffComments(this._changeNum),
         this._getDiffDrafts(),
         this.$.restAPI.getDiffRobotComments(this._changeNum),
-      ]).then(function(results) {
-        var commentMap = {};
-        results.forEach(function(response) {
-          for (var path in response) {
+      ]).then(results => {
+        const commentMap = {};
+        for (const response of results) {
+          for (const path in response) {
             if (response.hasOwnProperty(path) &&
-                response[path].filter(filterByRange.bind(this)).length) {
+                response[path].filter(filterByRange).length) {
               commentMap[path] = true;
             }
           }
-        }.bind(this));
+        }
         return commentMap;
-      }.bind(this));
+      });
     },
 
-    _getDiffDrafts: function() {
-      return this._getLoggedIn().then(function(loggedIn) {
+    _getDiffDrafts() {
+      return this._getLoggedIn().then(loggedIn => {
         if (!loggedIn) { return Promise.resolve({}); }
         return this.$.restAPI.getDiffDrafts(this._changeNum);
-      }.bind(this));
+      });
     },
 
-    _computeCommentSkips: function(commentMap, fileList, path) {
-      var skips = {previous: null, next: null};
+    _computeCommentSkips(commentMap, fileList, path) {
+      const skips = {previous: null, next: null};
       if (!fileList.length) { return skips; }
-      var pathIndex = fileList.indexOf(path);
+      const pathIndex = fileList.indexOf(path);
 
       // Scan backward for the previous file.
-      for (var i = pathIndex - 1; i >= 0; i--) {
+      for (let i = pathIndex - 1; i >= 0; i--) {
         if (commentMap[fileList[i]]) {
           skips.previous = fileList[i];
           break;
@@ -705,7 +707,7 @@
       }
 
       // Scan forward for the next file.
-      for (i = pathIndex + 1; i < fileList.length; i++) {
+      for (let i = pathIndex + 1; i < fileList.length; i++) {
         if (commentMap[fileList[i]]) {
           skips.next = fileList[i];
           break;
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.html b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.html
index 663cd3baa8..625af35e65 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.html
@@ -41,34 +41,34 @@ limitations under the License.
 </test-fixture>
 
 <script>
-  suite('gr-diff-view tests', function() {
-    var element;
-    var sandbox;
+  suite('gr-diff-view tests', () => {
+    let element;
+    let sandbox;
 
-    setup(function() {
+    setup(() => {
       sandbox = sinon.sandbox.create();
 
       stub('gr-rest-api-interface', {
-        getLoggedIn: function() { return Promise.resolve(false); },
-        getProjectConfig: function() { return Promise.resolve({}); },
-        getDiffChangeDetail: function() { return Promise.resolve(null); },
-        getChangeFiles: function() { return Promise.resolve({}); },
-        saveFileReviewed: function() { return Promise.resolve(); },
+        getLoggedIn() { return Promise.resolve(false); },
+        getProjectConfig() { return Promise.resolve({}); },
+        getDiffChangeDetail() { return Promise.resolve(null); },
+        getChangeFiles() { return Promise.resolve({}); },
+        saveFileReviewed() { return Promise.resolve(); },
       });
       element = fixture('basic');
     });
 
-    teardown(function() {
+    teardown(() => {
       sandbox.restore();
     });
 
-    test('toggle left diff with a hotkey', function() {
-      var toggleLeftDiffStub = sandbox.stub(element.$.diff, 'toggleLeftDiff');
+    test('toggle left diff with a hotkey', () => {
+      const toggleLeftDiffStub = sandbox.stub(element.$.diff, 'toggleLeftDiff');
       MockInteractions.pressAndReleaseKeyOn(element, 65, 'shift', 'a');
       assert.isTrue(toggleLeftDiffStub.calledOnce);
     });
 
-    test('keyboard shortcuts', function() {
+    test('keyboard shortcuts', () => {
       element._changeNum = '42';
       element._patchRange = {
         basePatchNum: 'PARENT',
@@ -83,7 +83,7 @@ limitations under the License.
       element._path = 'glados.txt';
       element.changeViewState.selectedFileIndex = 1;
 
-      var showStub = sandbox.stub(page, 'show');
+      const showStub = sandbox.stub(page, 'show');
       MockInteractions.pressAndReleaseKeyOn(element, 85, null, 'u');
       assert(showStub.lastCall.calledWithExactly('/c/42/'),
           'Should navigate to /c/42/');
@@ -111,13 +111,14 @@ limitations under the License.
           'Should navigate to /c/42/');
       assert.equal(element.changeViewState.selectedFileIndex, 0);
 
-      var showPrefsStub = sandbox.stub(element.$.diffPreferences.$.prefsOverlay,
-          'open', function() { return Promise.resolve({}); });
+      const showPrefsStub =
+          sandbox.stub(element.$.diffPreferences.$.prefsOverlay, 'open',
+              () => Promise.resolve());
 
       MockInteractions.pressAndReleaseKeyOn(element, 188, null, ',');
       assert(showPrefsStub.calledOnce);
 
-      var scrollStub = sandbox.stub(element.$.cursor, 'moveToNextChunk');
+      let scrollStub = sandbox.stub(element.$.cursor, 'moveToNextChunk');
       MockInteractions.pressAndReleaseKeyOn(element, 78, null, 'n');
       assert(scrollStub.calledOnce);
 
@@ -134,7 +135,7 @@ limitations under the License.
       MockInteractions.pressAndReleaseKeyOn(element, 80, 'shift', 'p');
       assert(scrollStub.calledOnce);
 
-      var computeContainerClassStub = sandbox.stub(element.$.diff,
+      const computeContainerClassStub = sandbox.stub(element.$.diff,
           '_computeContainerClass');
       MockInteractions.pressAndReleaseKeyOn(element, 74, null, 'j');
       assert(computeContainerClassStub.lastCall.calledWithExactly(
@@ -145,7 +146,7 @@ limitations under the License.
           false, 'SIDE_BY_SIDE', false));
     });
 
-    test('keyboard shortcuts with patch range', function() {
+    test('keyboard shortcuts with patch range', () => {
       element._changeNum = '42';
       element._patchRange = {
         basePatchNum: '5',
@@ -159,7 +160,7 @@ limitations under the License.
       element._fileList = ['chell.go', 'glados.txt', 'wheatley.md'];
       element._path = 'glados.txt';
 
-      var showStub = sandbox.stub(page, 'show');
+      const showStub = sandbox.stub(page, 'show');
 
       MockInteractions.pressAndReleaseKeyOn(element, 65, null, 'a');
       assert.isTrue(showStub.notCalled, 'The `a` keyboard shortcut should ' +
@@ -198,7 +199,7 @@ limitations under the License.
           'Should navigate to /c/42/5..10');
     });
 
-    test('keyboard shortcuts with old patch number', function() {
+    test('keyboard shortcuts with old patch number', () => {
       element._changeNum = '42';
       element._patchRange = {
         basePatchNum: 'PARENT',
@@ -213,7 +214,7 @@ limitations under the License.
       element._fileList = ['chell.go', 'glados.txt', 'wheatley.md'];
       element._path = 'glados.txt';
 
-      var showStub = sandbox.stub(page, 'show');
+      const showStub = sandbox.stub(page, 'show');
 
       MockInteractions.pressAndReleaseKeyOn(element, 65, null, 'a');
       assert.isTrue(showStub.notCalled, 'The `a` keyboard shortcut should ' +
@@ -252,8 +253,7 @@ limitations under the License.
           'Should navigate to /c/42/1');
     });
 
-    test('Diff preferences hidden when no prefs or logged out',
-        function() {
+    test('Diff preferences hidden when no prefs or logged out', () => {
       element._loggedIn = false;
       flushAsynchronousOperations();
       assert.isTrue(element.$.diffPrefsContainer.hidden);
@@ -263,7 +263,7 @@ limitations under the License.
       assert.isTrue(element.$.diffPrefsContainer.hidden);
 
       element._loggedIn = false;
-      element._prefs = {'font_size': '12'};
+      element._prefs = {font_size: '12'};
       flushAsynchronousOperations();
       assert.isTrue(element.$.diffPrefsContainer.hidden);
 
@@ -272,11 +272,12 @@ limitations under the License.
       assert.isFalse(element.$.diffPrefsContainer.hidden);
     });
 
-    test('prefsButton opens gr-diff-preferences', function() {
-      var handlePrefsTapSpy = sandbox.spy(element, '_handlePrefsTap');
-      var overlayOpenStub = sandbox.stub(element.$.diffPreferences,
+    test('prefsButton opens gr-diff-preferences', () => {
+      const handlePrefsTapSpy = sandbox.spy(element, '_handlePrefsTap');
+      const overlayOpenStub = sandbox.stub(element.$.diffPreferences,
           'open');
-      var prefsButton = Polymer.dom(element.root).querySelector('.prefsButton');
+      const prefsButton =
+          Polymer.dom(element.root).querySelector('.prefsButton');
 
       MockInteractions.tap(prefsButton);
 
@@ -284,7 +285,7 @@ limitations under the License.
       assert.isTrue(overlayOpenStub.called);
     });
 
-    test('go up to change via kb without change loaded', function() {
+    test('go up to change via kb without change loaded', () => {
       element._changeNum = '42';
       element._patchRange = {
         basePatchNum: 'PARENT',
@@ -294,7 +295,7 @@ limitations under the License.
       element._fileList = ['chell.go', 'glados.txt', 'wheatley.md'];
       element._path = 'glados.txt';
 
-      var showStub = sandbox.stub(page, 'show');
+      const showStub = sandbox.stub(page, 'show');
 
       MockInteractions.pressAndReleaseKeyOn(element, 65, null, 'a');
       assert.isTrue(showStub.notCalled, 'The `a` keyboard shortcut should ' +
@@ -333,7 +334,7 @@ limitations under the License.
           'Should navigate to /c/42/1');
     });
 
-    test('jump to file dropdown', function() {
+    test('jump to file dropdown', () => {
       element._changeNum = '42';
       element._patchRange = {
         basePatchNum: 'PARENT',
@@ -342,7 +343,7 @@ limitations under the License.
       element._fileList = ['chell.go', 'glados.txt', 'wheatley.md'];
       element._path = 'glados.txt';
       flushAsynchronousOperations();
-      var linkEls =
+      const linkEls =
           Polymer.dom(element.root).querySelectorAll('.dropdown-content > a');
       assert.equal(linkEls.length, 3);
       assert.isFalse(linkEls[0].hasAttribute('selected'));
@@ -363,7 +364,7 @@ limitations under the License.
           'Merge list');
     });
 
-    test('jump to file dropdown with patch range', function() {
+    test('jump to file dropdown with patch range', () => {
       element._changeNum = '42';
       element._patchRange = {
         basePatchNum: '5',
@@ -372,7 +373,7 @@ limitations under the License.
       element._fileList = ['chell.go', 'glados.txt', 'wheatley.md'];
       element._path = 'glados.txt';
       flushAsynchronousOperations();
-      var linkEls =
+      const linkEls =
           Polymer.dom(element.root).querySelectorAll('.dropdown-content > a');
       assert.equal(linkEls.length, 3);
       assert.isFalse(linkEls[0].hasAttribute('selected'));
@@ -386,7 +387,7 @@ limitations under the License.
       assert.equal(linkEls[2].getAttribute('href'), '/c/42/5..10/wheatley.md');
     });
 
-    test('prev/up/next links', function() {
+    test('prev/up/next links', () => {
       element._changeNum = '42';
       element._patchRange = {
         basePatchNum: 'PARENT',
@@ -400,7 +401,7 @@ limitations under the License.
       element._fileList = ['chell.go', 'glados.txt', 'wheatley.md'];
       element._path = 'glados.txt';
       flushAsynchronousOperations();
-      var linkEls = Polymer.dom(element.root).querySelectorAll('.navLink');
+      const linkEls = Polymer.dom(element.root).querySelectorAll('.navLink');
       assert.equal(linkEls.length, 3);
       assert.equal(linkEls[0].getAttribute('href'), '/c/42/10/chell.go');
       assert.equal(linkEls[1].getAttribute('href'), '/c/42/');
@@ -422,7 +423,7 @@ limitations under the License.
       assert.equal(linkEls[2].getAttribute('href'), '/c/42/10/chell.go');
     });
 
-    test('download link', function() {
+    test('download link', () => {
       element._changeNum = '42';
       element._patchRange = {
         basePatchNum: 'PARENT',
@@ -435,7 +436,7 @@ limitations under the License.
           '/changes/42/revisions/10/patch?zip&path=glados.txt');
     });
 
-    test('prev/up/next links with patch range', function() {
+    test('prev/up/next links with patch range', () => {
       element._changeNum = '42';
       element._patchRange = {
         basePatchNum: '5',
@@ -450,7 +451,7 @@ limitations under the License.
       element._fileList = ['chell.go', 'glados.txt', 'wheatley.md'];
       element._path = 'glados.txt';
       flushAsynchronousOperations();
-      var linkEls = Polymer.dom(element.root).querySelectorAll('.navLink');
+      const linkEls = Polymer.dom(element.root).querySelectorAll('.navLink');
       assert.equal(linkEls.length, 3);
       assert.equal(linkEls[0].getAttribute('href'), '/c/42/5..10/chell.go');
       assert.equal(linkEls[1].getAttribute('href'), '/c/42/5..10');
@@ -467,7 +468,7 @@ limitations under the License.
       assert.equal(linkEls[2].getAttribute('href'), '/c/42/5..10/glados.txt');
     });
 
-    test('file review status', function(done) {
+    test('file review status', done => {
       element._loggedIn = true;
       element._changeNum = '42';
       element._patchRange = {
@@ -476,11 +477,11 @@ limitations under the License.
       };
       element._fileList = ['/COMMIT_MSG'];
       element._path = '/COMMIT_MSG';
-      var saveReviewedStub = sandbox.stub(element, '_saveReviewedState',
-          function() { return Promise.resolve(); });
+      const saveReviewedStub = sandbox.stub(element, '_saveReviewedState',
+          () => Promise.resolve());
 
-      flush(function() {
-        var commitMsg = Polymer.dom(element.root).querySelector(
+      flush(() => {
+        const commitMsg = Polymer.dom(element.root).querySelector(
             'input[type="checkbox"]');
 
         assert.isTrue(commitMsg.checked);
@@ -496,9 +497,9 @@ limitations under the License.
       });
     });
 
-    test('diff mode selector correctly toggles the diff', function() {
-      var select = element.$.modeSelect;
-      var diffDisplay = element.$.diff;
+    test('diff mode selector correctly toggles the diff', () => {
+      const select = element.$.modeSelect;
+      const diffDisplay = element.$.diff;
       element._userPrefs = {default_diff_view: 'SIDE_BY_SIDE'};
 
       // The mode selected in the view state reflects the selected option.
@@ -509,7 +510,7 @@ limitations under the License.
       assert.equal(select.value, diffDisplay.viewMode);
 
       // We will simulate a user change of the selected mode.
-      var newMode = 'UNIFIED_DIFF';
+      const newMode = 'UNIFIED_DIFF';
       // Set the actual value of the select, and simulate the change event.
       select.value = newMode;
       element.fire('change', {}, {node: select});
@@ -520,17 +521,16 @@ limitations under the License.
       assert.equal(element._getDiffViewMode(), diffDisplay.viewMode);
     });
 
-    test('diff mode selector initializes from preferences', function() {
-      var resolvePrefs;
-      var prefsPromise = new Promise(function(resolve) {
+    test('diff mode selector initializes from preferences', () => {
+      let resolvePrefs;
+      const prefsPromise = new Promise(resolve => {
         resolvePrefs = resolve;
       });
-      var getPreferencesStub = sandbox.stub(element.$.restAPI, 'getPreferences',
-          function() { return prefsPromise; });
+      sandbox.stub(element.$.restAPI, 'getPreferences', () => prefsPromise);
 
       // Attach a new gr-diff-view so we can intercept the preferences fetch.
-      var view = document.createElement('gr-diff-view');
-      var select = view.$.modeSelect;
+      const view = document.createElement('gr-diff-view');
+      const select = view.$.modeSelect;
       fixture('blank').appendChild(view);
       flushAsynchronousOperations();
 
@@ -543,7 +543,7 @@ limitations under the License.
       assert.equal(select.value, 'SIDE_BY_SIDE');
     });
 
-    test('_loadHash', function() {
+    test('_loadHash', () => {
       assert.isNotOk(element.$.cursor.initialLineNumber);
 
       // Ignores invalid hashes:
@@ -566,32 +566,31 @@ limitations under the License.
       assert.equal(element.$.cursor.side, 'left');
     });
 
-    test('_shortenPath with long path should add ellipsis', function() {
-      var path =
-          'level1/level2/level3/level4/file.js';
-      var shortenedPath = util.truncatePath(path);
+    test('_shortenPath with long path should add ellipsis', () => {
+      let path = 'level1/level2/level3/level4/file.js';
+      let shortenedPath = util.truncatePath(path);
       // The expected path is truncated with an ellipsis.
-      var expectedPath = '\u2026/file.js';
+      const expectedPath = '\u2026/file.js';
       assert.equal(shortenedPath, expectedPath);
 
-      var path = 'level2/file.js';
-      var shortenedPath = util.truncatePath(path);
+      path = 'level2/file.js';
+      shortenedPath = util.truncatePath(path);
       assert.equal(shortenedPath, expectedPath);
     });
 
-    test('_shortenPath with short path should not add ellipsis', function() {
-      var path = 'file.js';
-      var expectedPath = 'file.js';
-      var shortenedPath = util.truncatePath(path);
+    test('_shortenPath with short path should not add ellipsis', () => {
+      const path = 'file.js';
+      const expectedPath = 'file.js';
+      const shortenedPath = util.truncatePath(path);
       assert.equal(shortenedPath, expectedPath);
     });
 
-    test('_onLineSelected', function() {
-      var replaceStateStub = sandbox.stub(history, 'replaceState');
-      var moveStub = sandbox.stub(element.$.cursor, 'moveToLineNumber');
+    test('_onLineSelected', () => {
+      const replaceStateStub = sandbox.stub(history, 'replaceState');
+      const moveStub = sandbox.stub(element.$.cursor, 'moveToLineNumber');
 
-      var e = {};
-      var detail = {number: 123, side: 'right'};
+      const e = {};
+      const detail = {number: 123, side: 'right'};
 
       element._onLineSelected(e, detail);
 
@@ -602,15 +601,15 @@ limitations under the License.
       assert.isTrue(replaceStateStub.called);
     });
 
-    test('_getDiffURL encodes special characters', function() {
-      var changeNum = 123;
-      var patchRange = {basePatchNum: 123, patchNum: 456};
-      var path = 'c++/cpp.cpp';
+    test('_getDiffURL encodes special characters', () => {
+      const changeNum = 123;
+      const patchRange = {basePatchNum: 123, patchNum: 456};
+      const path = 'c++/cpp.cpp';
       assert.equal(element._getDiffURL(changeNum, patchRange, path),
           '/c/123/123..456/c%252B%252B/cpp.cpp');
     });
 
-    test('_getDiffViewMode', function() {
+    test('_getDiffViewMode', () => {
       // No user prefs or change view state set.
       assert.equal(element._getDiffViewMode(), 'SIDE_BY_SIDE');
 
@@ -623,22 +622,22 @@ limitations under the License.
       assert.equal(element._getDiffViewMode(), 'SIDE_BY_SIDE');
     });
 
-    suite('_loadCommentMap', function() {
-      test('empty', function(done) {
+    suite('_loadCommentMap', () => {
+      test('empty', done => {
         stub('gr-rest-api-interface', {
-          getDiffRobotComments: function() { return Promise.resolve({}); },
-          getDiffComments: function() { return Promise.resolve({}); },
+          getDiffRobotComments() { return Promise.resolve({}); },
+          getDiffComments() { return Promise.resolve({}); },
         });
-        element._loadCommentMap().then(function(map) {
+        element._loadCommentMap().then(map => {
           assert.equal(Object.keys(map).length, 0);
           done();
         });
       });
 
-      test('paths in patch range', function(done) {
+      test('paths in patch range', done => {
         stub('gr-rest-api-interface', {
-          getDiffRobotComments: function() { return Promise.resolve({}); },
-          getDiffComments: function() {
+          getDiffRobotComments() { return Promise.resolve({}); },
+          getDiffComments() {
             return Promise.resolve({
               'path/to/file/one.cpp': [{patch_set: 3, message: 'lorem'}],
               'path-to/file/two.py': [{patch_set: 5, message: 'ipsum'}],
@@ -650,17 +649,17 @@ limitations under the License.
           basePatchNum: '3',
           patchNum: '5',
         };
-        element._loadCommentMap().then(function(map) {
+        element._loadCommentMap().then(map => {
           assert.deepEqual(Object.keys(map),
               ['path/to/file/one.cpp', 'path-to/file/two.py']);
           done();
         });
       });
 
-      test('empty for paths outside patch range', function(done) {
+      test('empty for paths outside patch range', done => {
         stub('gr-rest-api-interface', {
-          getDiffRobotComments: function() { return Promise.resolve({}); },
-          getDiffComments: function() {
+          getDiffRobotComments() { return Promise.resolve({}); },
+          getDiffComments() {
             return Promise.resolve({
               'path/to/file/one.cpp': [{patch_set: 'PARENT', message: 'lorem'}],
               'path-to/file/two.py': [{patch_set: 2, message: 'ipsum'}],
@@ -672,35 +671,35 @@ limitations under the License.
           basePatchNum: '3',
           patchNum: '5',
         };
-        element._loadCommentMap().then(function(map) {
+        element._loadCommentMap().then(map => {
           assert.equal(Object.keys(map).length, 0);
           done();
         });
       });
     });
 
-    suite('_computeCommentSkips', function() {
-      test('empty file list', function() {
-        var commentMap = {
+    suite('_computeCommentSkips', () => {
+      test('empty file list', () => {
+        const commentMap = {
           'path/one.jpg': true,
           'path/three.wav': true,
         };
-        var path = 'path/two.m4v';
-        var fileList = [];
-        var result = element._computeCommentSkips(commentMap, fileList, path);
+        const path = 'path/two.m4v';
+        const fileList = [];
+        const result = element._computeCommentSkips(commentMap, fileList, path);
         assert.isNull(result.previous);
         assert.isNull(result.next);
       });
 
-      test('finds skips', function() {
-        var fileList = ['path/one.jpg', 'path/two.m4v', 'path/three.wav'];
-        var path = fileList[1];
-        var commentMap = {};
+      test('finds skips', () => {
+        const fileList = ['path/one.jpg', 'path/two.m4v', 'path/three.wav'];
+        let path = fileList[1];
+        const commentMap = {};
         commentMap[fileList[0]] = true;
         commentMap[fileList[1]] = false;
         commentMap[fileList[2]] = true;
 
-        var result = element._computeCommentSkips(commentMap, fileList, path);
+        let result = element._computeCommentSkips(commentMap, fileList, path);
         assert.equal(result.previous, fileList[0]);
         assert.equal(result.next, fileList[2]);