diff --git a/web/toolbar.js b/web/toolbar.js
index d30f168c8..5379cfae5 100644
--- a/web/toolbar.js
+++ b/web/toolbar.js
@@ -18,9 +18,9 @@ import {
   MIN_SCALE, noContextMenuHandler, NullL10n
 } from './ui_utils';
 
-var PAGE_NUMBER_LOADING_INDICATOR = 'visiblePageIsLoading';
-var SCALE_SELECT_CONTAINER_PADDING = 8;
-var SCALE_SELECT_PADDING = 22;
+const PAGE_NUMBER_LOADING_INDICATOR = 'visiblePageIsLoading';
+const SCALE_SELECT_CONTAINER_PADDING = 8;
+const SCALE_SELECT_PADDING = 22;
 
 /**
  * @typedef {Object} ToolbarOptions
@@ -46,18 +46,14 @@ var SCALE_SELECT_PADDING = 22;
  *   the page view.
  */
 
-/**
- * @class
- */
-var Toolbar = (function ToolbarClosure() {
+class Toolbar {
   /**
-   * @constructs Toolbar
    * @param {ToolbarOptions} options
    * @param {HTMLDivElement} mainContainer
    * @param {EventBus} eventBus
    * @param {IL10n} l10n - Localization service.
    */
-  function Toolbar(options, mainContainer, eventBus, l10n = NullL10n) {
+  constructor(options, mainContainer, eventBus, l10n = NullL10n) {
     this.toolbar = options.container;
     this.mainContainer = mainContainer;
     this.eventBus = eventBus;
@@ -71,211 +67,206 @@ var Toolbar = (function ToolbarClosure() {
     this._bindListeners();
   }
 
-  Toolbar.prototype = {
-    setPageNumber(pageNumber, pageLabel) {
-      this.pageNumber = pageNumber;
-      this.pageLabel = pageLabel;
-      this._updateUIState(false);
-    },
+  setPageNumber(pageNumber, pageLabel) {
+    this.pageNumber = pageNumber;
+    this.pageLabel = pageLabel;
+    this._updateUIState(false);
+  }
 
-    setPagesCount(pagesCount, hasPageLabels) {
-      this.pagesCount = pagesCount;
-      this.hasPageLabels = hasPageLabels;
-      this._updateUIState(true);
-    },
+  setPagesCount(pagesCount, hasPageLabels) {
+    this.pagesCount = pagesCount;
+    this.hasPageLabels = hasPageLabels;
+    this._updateUIState(true);
+  }
 
-    setPageScale(pageScaleValue, pageScale) {
-      this.pageScaleValue = pageScaleValue;
-      this.pageScale = pageScale;
-      this._updateUIState(false);
-    },
+  setPageScale(pageScaleValue, pageScale) {
+    this.pageScaleValue = pageScaleValue;
+    this.pageScale = pageScale;
+    this._updateUIState(false);
+  }
 
-    reset() {
-      this.pageNumber = 0;
-      this.pageLabel = null;
-      this.hasPageLabels = false;
-      this.pagesCount = 0;
-      this.pageScaleValue = DEFAULT_SCALE_VALUE;
-      this.pageScale = DEFAULT_SCALE;
-      this._updateUIState(true);
-    },
+  reset() {
+    this.pageNumber = 0;
+    this.pageLabel = null;
+    this.hasPageLabels = false;
+    this.pagesCount = 0;
+    this.pageScaleValue = DEFAULT_SCALE_VALUE;
+    this.pageScale = DEFAULT_SCALE;
+    this._updateUIState(true);
+  }
 
-    _bindListeners: function Toolbar_bindClickListeners() {
-      var eventBus = this.eventBus;
-      var self = this;
-      var items = this.items;
+  _bindListeners() {
+    let eventBus = this.eventBus;
+    let self = this;
+    let items = this.items;
 
-      items.previous.addEventListener('click', function() {
-        eventBus.dispatch('previouspage');
+    items.previous.addEventListener('click', function() {
+      eventBus.dispatch('previouspage');
+    });
+
+    items.next.addEventListener('click', function() {
+      eventBus.dispatch('nextpage');
+    });
+
+    items.zoomIn.addEventListener('click', function() {
+      eventBus.dispatch('zoomin');
+    });
+
+    items.zoomOut.addEventListener('click', function() {
+      eventBus.dispatch('zoomout');
+    });
+
+    items.pageNumber.addEventListener('click', function() {
+      this.select();
+    });
+
+    items.pageNumber.addEventListener('change', function() {
+      eventBus.dispatch('pagenumberchanged', {
+        source: self,
+        value: this.value,
       });
+    });
 
-      items.next.addEventListener('click', function() {
-        eventBus.dispatch('nextpage');
-      });
-
-      items.zoomIn.addEventListener('click', function() {
-        eventBus.dispatch('zoomin');
-      });
-
-      items.zoomOut.addEventListener('click', function() {
-        eventBus.dispatch('zoomout');
-      });
-
-      items.pageNumber.addEventListener('click', function() {
-        this.select();
-      });
-
-      items.pageNumber.addEventListener('change', function() {
-        eventBus.dispatch('pagenumberchanged', {
-          source: self,
-          value: this.value,
-        });
-      });
-
-      items.scaleSelect.addEventListener('change', function() {
-        if (this.value === 'custom') {
-          return;
-        }
-        eventBus.dispatch('scalechanged', {
-          source: self,
-          value: this.value,
-        });
-      });
-
-      items.presentationModeButton.addEventListener('click',
-          function (e) {
-        eventBus.dispatch('presentationmode');
-      });
-
-      items.openFile.addEventListener('click', function (e) {
-        eventBus.dispatch('openfile');
-      });
-
-      items.print.addEventListener('click', function (e) {
-        eventBus.dispatch('print');
-      });
-
-      items.download.addEventListener('click', function (e) {
-        eventBus.dispatch('download');
-      });
-
-      // Suppress context menus for some controls
-      items.scaleSelect.oncontextmenu = noContextMenuHandler;
-
-      eventBus.on('localized', (evt) => {
-        this._localized();
-      });
-    },
-
-    _localized: function Toolbar_localized() {
-      this._wasLocalized = true;
-      this._adjustScaleWidth();
-      this._updateUIState(true);
-    },
-
-    _updateUIState: function Toolbar_updateUIState(resetNumPages) {
-      if (!this._wasLocalized) {
-        // Don't update UI state until we will localize the toolbar.
+    items.scaleSelect.addEventListener('change', function() {
+      if (this.value === 'custom') {
         return;
       }
+      eventBus.dispatch('scalechanged', {
+        source: self,
+        value: this.value,
+      });
+    });
 
-      let selectScaleOption = (value, scale) => {
-        let customScale = Math.round(scale * 10000) / 100;
-        this.l10n.get('page_scale_percent', { scale: customScale, },
-                      '{{scale}}%').then((msg) => {
-          let options = items.scaleSelect.options;
-          let predefinedValueFound = false;
-          for (let i = 0, ii = options.length; i < ii; i++) {
-            let option = options[i];
-            if (option.value !== value) {
-              option.selected = false;
-              continue;
-            }
-            option.selected = true;
-            predefinedValueFound = true;
+    items.presentationModeButton.addEventListener('click', function() {
+      eventBus.dispatch('presentationmode');
+    });
+
+    items.openFile.addEventListener('click', function() {
+      eventBus.dispatch('openfile');
+    });
+
+    items.print.addEventListener('click', function() {
+      eventBus.dispatch('print');
+    });
+
+    items.download.addEventListener('click', function() {
+      eventBus.dispatch('download');
+    });
+
+    // Suppress context menus for some controls.
+    items.scaleSelect.oncontextmenu = noContextMenuHandler;
+
+    eventBus.on('localized', () => {
+      this._localized();
+    });
+  }
+
+  _localized() {
+    this._wasLocalized = true;
+    this._adjustScaleWidth();
+    this._updateUIState(true);
+  }
+
+  _updateUIState(resetNumPages = false) {
+    if (!this._wasLocalized) {
+      // Don't update the UI state until we localize the toolbar.
+      return;
+    }
+
+    let selectScaleOption = (value, scale) => {
+      let customScale = Math.round(scale * 10000) / 100;
+      this.l10n.get('page_scale_percent', { scale: customScale, },
+                    '{{scale}}%').then((msg) => {
+        let options = items.scaleSelect.options;
+        let predefinedValueFound = false;
+        for (let i = 0, ii = options.length; i < ii; i++) {
+          let option = options[i];
+          if (option.value !== value) {
+            option.selected = false;
+            continue;
           }
-          if (!predefinedValueFound) {
-            items.customScaleOption.textContent = msg;
-            items.customScaleOption.selected = true;
-          }
-        });
-      };
-
-      var pageNumber = this.pageNumber;
-      var scaleValue = (this.pageScaleValue || this.pageScale).toString();
-      var scale = this.pageScale;
-
-      var items = this.items;
-      var pagesCount = this.pagesCount;
-
-      if (resetNumPages) {
-        if (this.hasPageLabels) {
-          items.pageNumber.type = 'text';
-        } else {
-          items.pageNumber.type = 'number';
-          this.l10n.get('of_pages', { pagesCount, }, 'of {{pagesCount}}').
-              then((msg) => {
-            items.numPages.textContent = msg;
-          });
+          option.selected = true;
+          predefinedValueFound = true;
         }
-        items.pageNumber.max = pagesCount;
-      }
+        if (!predefinedValueFound) {
+          items.customScaleOption.textContent = msg;
+          items.customScaleOption.selected = true;
+        }
+      });
+    };
 
+    let pageNumber = this.pageNumber;
+    let scaleValue = (this.pageScaleValue || this.pageScale).toString();
+    let scale = this.pageScale;
+
+    let items = this.items;
+    let pagesCount = this.pagesCount;
+
+    if (resetNumPages) {
       if (this.hasPageLabels) {
-        items.pageNumber.value = this.pageLabel;
-        this.l10n.get('page_of_pages', { pageNumber, pagesCount, },
-                      '({{pageNumber}} of {{pagesCount}})').
+        items.pageNumber.type = 'text';
+      } else {
+        items.pageNumber.type = 'number';
+        this.l10n.get('of_pages', { pagesCount, }, 'of {{pagesCount}}').
             then((msg) => {
           items.numPages.textContent = msg;
         });
-      } else {
-        items.pageNumber.value = pageNumber;
       }
+      items.pageNumber.max = pagesCount;
+    }
 
-      items.previous.disabled = (pageNumber <= 1);
-      items.next.disabled = (pageNumber >= pagesCount);
-
-      items.zoomOut.disabled = (scale <= MIN_SCALE);
-      items.zoomIn.disabled = (scale >= MAX_SCALE);
-
-      selectScaleOption(scaleValue, scale);
-    },
-
-    updateLoadingIndicatorState:
-        function Toolbar_updateLoadingIndicatorState(loading) {
-      var pageNumberInput = this.items.pageNumber;
-
-      if (loading) {
-        pageNumberInput.classList.add(PAGE_NUMBER_LOADING_INDICATOR);
-      } else {
-        pageNumberInput.classList.remove(PAGE_NUMBER_LOADING_INDICATOR);
-      }
-    },
-
-    _adjustScaleWidth: function Toolbar_adjustScaleWidth() {
-      var container = this.items.scaleSelectContainer;
-      var select = this.items.scaleSelect;
-      animationStarted.then(function() {
-        // Adjust the width of the zoom box to fit the content.
-        // Note: If the window is narrow enough that the zoom box is not
-        //       visible, we temporarily show it to be able to adjust its width.
-        if (container.clientWidth === 0) {
-          container.setAttribute('style', 'display: inherit;');
-        }
-        if (container.clientWidth > 0) {
-          select.setAttribute('style', 'min-width: inherit;');
-          var width = select.clientWidth + SCALE_SELECT_CONTAINER_PADDING;
-          select.setAttribute('style', 'min-width: ' +
-                                      (width + SCALE_SELECT_PADDING) + 'px;');
-          container.setAttribute('style', 'min-width: ' + width + 'px; ' +
-                                          'max-width: ' + width + 'px;');
-        }
+    if (this.hasPageLabels) {
+      items.pageNumber.value = this.pageLabel;
+      this.l10n.get('page_of_pages', { pageNumber, pagesCount, },
+                    '({{pageNumber}} of {{pagesCount}})').
+          then((msg) => {
+        items.numPages.textContent = msg;
       });
-    },
-  };
+    } else {
+      items.pageNumber.value = pageNumber;
+    }
 
-  return Toolbar;
-})();
+    items.previous.disabled = (pageNumber <= 1);
+    items.next.disabled = (pageNumber >= pagesCount);
+
+    items.zoomOut.disabled = (scale <= MIN_SCALE);
+    items.zoomIn.disabled = (scale >= MAX_SCALE);
+
+    selectScaleOption(scaleValue, scale);
+  }
+
+  updateLoadingIndicatorState(loading = false) {
+    let pageNumberInput = this.items.pageNumber;
+
+    if (loading) {
+      pageNumberInput.classList.add(PAGE_NUMBER_LOADING_INDICATOR);
+    } else {
+      pageNumberInput.classList.remove(PAGE_NUMBER_LOADING_INDICATOR);
+    }
+  }
+
+  _adjustScaleWidth() {
+    let container = this.items.scaleSelectContainer;
+    let select = this.items.scaleSelect;
+
+    animationStarted.then(function() {
+      // Adjust the width of the zoom box to fit the content.
+      // Note: If the window is narrow enough that the zoom box is not
+      //       visible, we temporarily show it to be able to adjust its width.
+      if (container.clientWidth === 0) {
+        container.setAttribute('style', 'display: inherit;');
+      }
+      if (container.clientWidth > 0) {
+        select.setAttribute('style', 'min-width: inherit;');
+        let width = select.clientWidth + SCALE_SELECT_CONTAINER_PADDING;
+        select.setAttribute('style', 'min-width: ' +
+                                     (width + SCALE_SELECT_PADDING) + 'px;');
+        container.setAttribute('style', 'min-width: ' + width + 'px; ' +
+                                        'max-width: ' + width + 'px;');
+      }
+    });
+  }
+}
 
 export {
   Toolbar,