diff --git a/ui/file_manager/file_manager/foreground/js/mock_thumbnail_loader.js b/ui/file_manager/file_manager/foreground/js/mock_thumbnail_loader.js
index 288acfdce8b2c4..a2c1542a1d906d 100644
--- a/ui/file_manager/file_manager/foreground/js/mock_thumbnail_loader.js
+++ b/ui/file_manager/file_manager/foreground/js/mock_thumbnail_loader.js
@@ -4,19 +4,39 @@
 
 /**
  * Mock thumbnail loader.
- *
- * @param {Entry} entry An entry.
- * @param {ThumbnailLoader.LoaderType=} opt_loaderType Loader type.
- * @param {Object=} opt_metadata Metadata.
- * @param {string=} opt_mediaType Media type.
- * @param {Array<ThumbnailLoader.LoadTarget>=} opt_loadTargets Load targets.
- * @param {number=} opt_priority Priority.
- * @constructor
  */
-function MockThumbnailLoader(
-    entry, opt_loaderType, opt_metadata, opt_mediaType, opt_loadTargets,
-    opt_priority) {
-  this.entry_ = entry;
+class MockThumbnailLoader {
+  /**
+   * @param {Entry} entry An entry.
+   * @param {ThumbnailLoader.LoaderType=} opt_loaderType Loader type.
+   * @param {Object=} opt_metadata Metadata.
+   * @param {string=} opt_mediaType Media type.
+   * @param {Array<ThumbnailLoader.LoadTarget>=} opt_loadTargets Load targets.
+   * @param {number=} opt_priority Priority.
+   */
+  constructor(
+      entry, opt_loaderType, opt_metadata, opt_mediaType, opt_loadTargets,
+      opt_priority) {
+    this.entry_ = entry;
+  }
+
+  /**
+   * Loads thumbnail as data url.
+   *
+   * @return {!Promise<{data:?string, width:number, height:number}>} A
+   *     promise which is resolved with data url.
+   */
+  loadAsDataUrl() {
+    if (MockThumbnailLoader.errorUrls.indexOf(this.entry_.toURL()) !== -1) {
+      throw new Error('Failed to load thumbnail.');
+    }
+
+    return Promise.resolve({
+      data: MockThumbnailLoader.testImageDataUrl,
+      width: MockThumbnailLoader.testImageWidth,
+      height: MockThumbnailLoader.testImageHeight
+    });
+  }
 }
 
 /**
@@ -42,21 +62,3 @@ MockThumbnailLoader.testImageHeight = 0;
  * @private {Array<string>}
  */
 MockThumbnailLoader.errorUrls = [];
-
-/**
- * Loads thumbnail as data url.
- *
- * @return {!Promise<{data:?string, width:number, height:number}>} A
- *     promise which is resolved with data url.
- */
-MockThumbnailLoader.prototype.loadAsDataUrl = function() {
-  if (MockThumbnailLoader.errorUrls.indexOf(this.entry_.toURL()) !== -1) {
-    throw new Error('Failed to load thumbnail.');
-  }
-
-  return Promise.resolve({
-    data: MockThumbnailLoader.testImageDataUrl,
-    width: MockThumbnailLoader.testImageWidth,
-    height: MockThumbnailLoader.testImageHeight
-  });
-};
diff --git a/ui/file_manager/file_manager/foreground/js/selection_menu_controller.js b/ui/file_manager/file_manager/foreground/js/selection_menu_controller.js
index 1993848f389c8d..1d852317d90cfa 100644
--- a/ui/file_manager/file_manager/foreground/js/selection_menu_controller.js
+++ b/ui/file_manager/file_manager/foreground/js/selection_menu_controller.js
@@ -2,51 +2,53 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-/**
- * @param {!cr.ui.MenuButton} selectionMenuButton
- * @param {!cr.ui.Menu} menu
- * @constructor
- * @struct
- */
-function SelectionMenuController(selectionMenuButton, menu) {
+class SelectionMenuController {
   /**
-   * @type {!FilesToggleRipple}
-   * @const
-   * @private
+   * @param {!cr.ui.MenuButton} selectionMenuButton
+   * @param {!cr.ui.Menu} menu
    */
-  this.toggleRipple_ =
-      /** @type {!FilesToggleRipple} */ (
-          queryRequiredElement('files-toggle-ripple', selectionMenuButton));
+  constructor(selectionMenuButton, menu) {
+    /**
+     * @type {!FilesToggleRipple}
+     * @const
+     * @private
+     */
+    this.toggleRipple_ =
+        /** @type {!FilesToggleRipple} */ (
+            queryRequiredElement('files-toggle-ripple', selectionMenuButton));
 
-  /**
-   * @type {!cr.ui.Menu}
-   * @const
-   */
-  this.menu_ = menu;
+    /**
+     * @type {!cr.ui.Menu}
+     * @const
+     */
+    this.menu_ = menu;
 
-  selectionMenuButton.addEventListener('menushow', this.onShowMenu_.bind(this));
-  selectionMenuButton.addEventListener('menuhide', this.onHideMenu_.bind(this));
-}
+    selectionMenuButton.addEventListener(
+        'menushow', this.onShowMenu_.bind(this));
+    selectionMenuButton.addEventListener(
+        'menuhide', this.onHideMenu_.bind(this));
+  }
 
-/**
- * @private
- */
-SelectionMenuController.prototype.onShowMenu_ = function() {
-  this.menu_.classList.toggle('toolbar-menu', true);
-  this.toggleRipple_.activated = true;
-  // crbug.com 752035 focus still on button, get rid of the tooltip
-  document.querySelector('files-tooltip').hideTooltip();
-};
+  /**
+   * @private
+   */
+  onShowMenu_() {
+    this.menu_.classList.toggle('toolbar-menu', true);
+    this.toggleRipple_.activated = true;
+    // crbug.com 752035 focus still on button, get rid of the tooltip
+    document.querySelector('files-tooltip').hideTooltip();
+  }
 
-/**
- * @private
- */
-SelectionMenuController.prototype.onHideMenu_ = function() {
-  // If menu is animating to close, then do not remove 'toolbar-menu' yet, it
-  // will be removed at the end of FilesMenuItem.setMenuAsAnimating_ to avoid
-  // flicker.  See crbug.com/862926.
-  if (!this.menu_.classList.contains('animating')) {
-    this.menu_.classList.toggle('toolbar-menu', false);
+  /**
+   * @private
+   */
+  onHideMenu_() {
+    // If menu is animating to close, then do not remove 'toolbar-menu' yet, it
+    // will be removed at the end of FilesMenuItem.setMenuAsAnimating_ to avoid
+    // flicker.  See crbug.com/862926.
+    if (!this.menu_.classList.contains('animating')) {
+      this.menu_.classList.toggle('toolbar-menu', false);
+    }
+    this.toggleRipple_.activated = false;
   }
-  this.toggleRipple_.activated = false;
-};
+}