diff --git a/web/pdf_thumbnail_view.js b/web/pdf_thumbnail_view.js
index 1de4e530a..1c0c3a42f 100644
--- a/web/pdf_thumbnail_view.js
+++ b/web/pdf_thumbnail_view.js
@@ -19,8 +19,9 @@ import {
 import { getOutputScale, NullL10n } from './ui_utils';
 import { RenderingStates } from './pdf_rendering_queue';
 
-var THUMBNAIL_WIDTH = 98; // px
-var THUMBNAIL_CANVAS_BORDER_WIDTH = 1; // px
+const MAX_NUM_SCALING_STEPS = 3;
+const THUMBNAIL_CANVAS_BORDER_WIDTH = 1; // px
+const THUMBNAIL_WIDTH = 98; // px
 
 /**
  * @typedef {Object} PDFThumbnailViewOptions
@@ -31,7 +32,7 @@ var THUMBNAIL_CANVAS_BORDER_WIDTH = 1; // px
  * @property {PDFRenderingQueue} renderingQueue - The rendering queue object.
  * @property {boolean} disableCanvasToImageConversion - (optional) Don't convert
  *   the canvas thumbnails to images. This prevents `toDataURL` calls,
- *   but increases the overall memory usage. The default value is false.
+ *   but increases the overall memory usage. The default value is `false`.
  * @property {IL10n} l10n - Localization service.
  */
 
@@ -77,23 +78,14 @@ const TempImageFactory = (function TempImageFactoryClosure() {
 })();
 
 /**
- * @class
  * @implements {IRenderableView}
  */
-var PDFThumbnailView = (function PDFThumbnailViewClosure() {
+class PDFThumbnailView {
   /**
-   * @constructs PDFThumbnailView
    * @param {PDFThumbnailViewOptions} options
    */
-  function PDFThumbnailView(options) {
-    var container = options.container;
-    var id = options.id;
-    var defaultViewport = options.defaultViewport;
-    var linkService = options.linkService;
-    var renderingQueue = options.renderingQueue;
-    var disableCanvasToImageConversion =
-      options.disableCanvasToImageConversion || false;
-
+  constructor({ container, id, defaultViewport, linkService, renderingQueue,
+                disableCanvasToImageConversion = false, l10n = NullL10n, }) {
     this.id = id;
     this.renderingId = 'thumbnail' + id;
     this.pageLabel = null;
@@ -119,21 +111,21 @@ var PDFThumbnailView = (function PDFThumbnailViewClosure() {
     this.canvasHeight = (this.canvasWidth / this.pageRatio) | 0;
     this.scale = this.canvasWidth / this.pageWidth;
 
-    this.l10n = options.l10n || NullL10n;
+    this.l10n = l10n;
 
-    var anchor = document.createElement('a');
+    let anchor = document.createElement('a');
     anchor.href = linkService.getAnchorUrl('#page=' + id);
     this.l10n.get('thumb_page_title', { page: id, }, 'Page {{page}}').
         then((msg) => {
       anchor.title = msg;
     });
-    anchor.onclick = function stopNavigation() {
+    anchor.onclick = function() {
       linkService.page = id;
       return false;
     };
     this.anchor = anchor;
 
-    var div = document.createElement('div');
+    let div = document.createElement('div');
     div.className = 'thumbnail';
     div.setAttribute('data-page-number', this.id);
     this.div = div;
@@ -144,9 +136,9 @@ var PDFThumbnailView = (function PDFThumbnailViewClosure() {
       div.classList.add('selected');
     }
 
-    var ring = document.createElement('div');
+    let ring = document.createElement('div');
     ring.className = 'thumbnailSelectionRing';
-    var borderAdjustment = 2 * THUMBNAIL_CANVAS_BORDER_WIDTH;
+    let borderAdjustment = 2 * THUMBNAIL_CANVAS_BORDER_WIDTH;
     ring.style.width = this.canvasWidth + borderAdjustment + 'px';
     ring.style.height = this.canvasHeight + borderAdjustment + 'px';
     this.ring = ring;
@@ -156,296 +148,288 @@ var PDFThumbnailView = (function PDFThumbnailViewClosure() {
     container.appendChild(anchor);
   }
 
-  PDFThumbnailView.prototype = {
-    setPdfPage: function PDFThumbnailView_setPdfPage(pdfPage) {
-      this.pdfPage = pdfPage;
-      this.pdfPageRotate = pdfPage.rotate;
-      var totalRotation = (this.rotation + this.pdfPageRotate) % 360;
-      this.viewport = pdfPage.getViewport(1, totalRotation);
-      this.reset();
-    },
+  setPdfPage(pdfPage) {
+    this.pdfPage = pdfPage;
+    this.pdfPageRotate = pdfPage.rotate;
+    let totalRotation = (this.rotation + this.pdfPageRotate) % 360;
+    this.viewport = pdfPage.getViewport(1, totalRotation);
+    this.reset();
+  }
 
-    reset: function PDFThumbnailView_reset() {
-      this.cancelRendering();
+  reset() {
+    this.cancelRendering();
 
-      this.pageWidth = this.viewport.width;
-      this.pageHeight = this.viewport.height;
-      this.pageRatio = this.pageWidth / this.pageHeight;
+    this.pageWidth = this.viewport.width;
+    this.pageHeight = this.viewport.height;
+    this.pageRatio = this.pageWidth / this.pageHeight;
 
-      this.canvasHeight = (this.canvasWidth / this.pageRatio) | 0;
-      this.scale = (this.canvasWidth / this.pageWidth);
+    this.canvasHeight = (this.canvasWidth / this.pageRatio) | 0;
+    this.scale = (this.canvasWidth / this.pageWidth);
 
-      this.div.removeAttribute('data-loaded');
-      var ring = this.ring;
-      var childNodes = ring.childNodes;
-      for (var i = childNodes.length - 1; i >= 0; i--) {
-        ring.removeChild(childNodes[i]);
-      }
-      var borderAdjustment = 2 * THUMBNAIL_CANVAS_BORDER_WIDTH;
-      ring.style.width = this.canvasWidth + borderAdjustment + 'px';
-      ring.style.height = this.canvasHeight + borderAdjustment + 'px';
+    this.div.removeAttribute('data-loaded');
+    let ring = this.ring;
+    let childNodes = ring.childNodes;
+    for (let i = childNodes.length - 1; i >= 0; i--) {
+      ring.removeChild(childNodes[i]);
+    }
+    let borderAdjustment = 2 * THUMBNAIL_CANVAS_BORDER_WIDTH;
+    ring.style.width = this.canvasWidth + borderAdjustment + 'px';
+    ring.style.height = this.canvasHeight + borderAdjustment + 'px';
 
-      if (this.canvas) {
-        // Zeroing the width and height causes Firefox to release graphics
-        // resources immediately, which can greatly reduce memory consumption.
-        this.canvas.width = 0;
-        this.canvas.height = 0;
-        delete this.canvas;
-      }
-      if (this.image) {
-        this.image.removeAttribute('src');
-        delete this.image;
-      }
-    },
+    if (this.canvas) {
+      // Zeroing the width and height causes Firefox to release graphics
+      // resources immediately, which can greatly reduce memory consumption.
+      this.canvas.width = 0;
+      this.canvas.height = 0;
+      delete this.canvas;
+    }
+    if (this.image) {
+      this.image.removeAttribute('src');
+      delete this.image;
+    }
+  }
 
-    update: function PDFThumbnailView_update(rotation) {
-      if (typeof rotation !== 'undefined') {
-        this.rotation = rotation;
-      }
-      var totalRotation = (this.rotation + this.pdfPageRotate) % 360;
-      this.viewport = this.viewport.clone({
-        scale: 1,
-        rotation: totalRotation,
-      });
-      this.reset();
-    },
+  update(rotation) {
+    if (typeof rotation !== 'undefined') {
+      this.rotation = rotation;
+    }
+    let totalRotation = (this.rotation + this.pdfPageRotate) % 360;
+    this.viewport = this.viewport.clone({
+      scale: 1,
+      rotation: totalRotation,
+    });
+    this.reset();
+  }
 
-    cancelRendering: function PDFThumbnailView_cancelRendering() {
-      if (this.renderTask) {
-        this.renderTask.cancel();
-        this.renderTask = null;
-      }
-      this.renderingState = RenderingStates.INITIAL;
-      this.resume = null;
-    },
+  cancelRendering() {
+    if (this.renderTask) {
+      this.renderTask.cancel();
+      this.renderTask = null;
+    }
+    this.renderingState = RenderingStates.INITIAL;
+    this.resume = null;
+  }
 
-    /**
-     * @private
-     */
-    _getPageDrawContext:
-        function PDFThumbnailView_getPageDrawContext(noCtxScale) {
-      var canvas = document.createElement('canvas');
-      // Keep the no-thumbnail outline visible, i.e. `data-loaded === false`,
-      // until rendering/image conversion is complete, to avoid display issues.
-      this.canvas = canvas;
+  /**
+   * @private
+   */
+  _getPageDrawContext(noCtxScale = false) {
+    let canvas = document.createElement('canvas');
+    // Keep the no-thumbnail outline visible, i.e. `data-loaded === false`,
+    // until rendering/image conversion is complete, to avoid display issues.
+    this.canvas = canvas;
+
+    if (typeof PDFJSDev === 'undefined' ||
+        PDFJSDev.test('MOZCENTRAL || FIREFOX || GENERIC')) {
+      canvas.mozOpaque = true;
+    }
+    let ctx = canvas.getContext('2d', { alpha: false, });
+    let outputScale = getOutputScale(ctx);
 
-      if (typeof PDFJSDev === 'undefined' ||
-          PDFJSDev.test('MOZCENTRAL || FIREFOX || GENERIC')) {
-        canvas.mozOpaque = true;
-      }
-      var ctx = canvas.getContext('2d', { alpha: false, });
-      var outputScale = getOutputScale(ctx);
+    canvas.width = (this.canvasWidth * outputScale.sx) | 0;
+    canvas.height = (this.canvasHeight * outputScale.sy) | 0;
+    canvas.style.width = this.canvasWidth + 'px';
+    canvas.style.height = this.canvasHeight + 'px';
 
-      canvas.width = (this.canvasWidth * outputScale.sx) | 0;
-      canvas.height = (this.canvasHeight * outputScale.sy) | 0;
-      canvas.style.width = this.canvasWidth + 'px';
-      canvas.style.height = this.canvasHeight + 'px';
+    if (!noCtxScale && outputScale.scaled) {
+      ctx.scale(outputScale.sx, outputScale.sy);
+    }
+    return ctx;
+  }
 
-      if (!noCtxScale && outputScale.scaled) {
-        ctx.scale(outputScale.sx, outputScale.sy);
-      }
-      return ctx;
-    },
+  /**
+   * @private
+   */
+  _convertCanvasToImage() {
+    if (!this.canvas) {
+      return;
+    }
+    if (this.renderingState !== RenderingStates.FINISHED) {
+      return;
+    }
+    let id = this.renderingId;
+    let className = 'thumbnailImage';
 
-    /**
-     * @private
-     */
-    _convertCanvasToImage: function PDFThumbnailView_convertCanvasToImage() {
-      if (!this.canvas) {
-        return;
-      }
-      if (this.renderingState !== RenderingStates.FINISHED) {
-        return;
-      }
-      var id = this.renderingId;
-      var className = 'thumbnailImage';
-
-      if (this.disableCanvasToImageConversion) {
-        this.canvas.id = id;
-        this.canvas.className = className;
-        this.l10n.get('thumb_page_canvas', { page: this.pageId, },
-                      'Thumbnail of Page {{page}}').then((msg) => {
-          this.canvas.setAttribute('aria-label', msg);
-        });
-
-        this.div.setAttribute('data-loaded', true);
-        this.ring.appendChild(this.canvas);
-        return;
-      }
-      var image = document.createElement('img');
-      image.id = id;
-      image.className = className;
+    if (this.disableCanvasToImageConversion) {
+      this.canvas.id = id;
+      this.canvas.className = className;
       this.l10n.get('thumb_page_canvas', { page: this.pageId, },
-        'Thumbnail of Page {{page}}').
-          then((msg) => {
-        image.setAttribute('aria-label', msg);
+                    'Thumbnail of Page {{page}}').then((msg) => {
+        this.canvas.setAttribute('aria-label', msg);
       });
 
-      image.style.width = this.canvasWidth + 'px';
-      image.style.height = this.canvasHeight + 'px';
-
-      image.src = this.canvas.toDataURL();
-      this.image = image;
-
       this.div.setAttribute('data-loaded', true);
-      this.ring.appendChild(image);
+      this.ring.appendChild(this.canvas);
+      return;
+    }
+    let image = document.createElement('img');
+    image.id = id;
+    image.className = className;
+    this.l10n.get('thumb_page_canvas', { page: this.pageId, },
+      'Thumbnail of Page {{page}}').
+        then((msg) => {
+      image.setAttribute('aria-label', msg);
+    });
 
-      // Zeroing the width and height causes Firefox to release graphics
-      // resources immediately, which can greatly reduce memory consumption.
-      this.canvas.width = 0;
-      this.canvas.height = 0;
-      delete this.canvas;
-    },
+    image.style.width = this.canvasWidth + 'px';
+    image.style.height = this.canvasHeight + 'px';
 
-    draw() {
-      if (this.renderingState !== RenderingStates.INITIAL) {
-        console.error('Must be in new state before drawing');
-        return Promise.resolve(undefined);
-      }
+    image.src = this.canvas.toDataURL();
+    this.image = image;
 
-      this.renderingState = RenderingStates.RUNNING;
-
-      let renderCapability = createPromiseCapability();
-
-      let finishRenderTask = (error) => {
-        // The renderTask may have been replaced by a new one, so only remove
-        // the reference to the renderTask if it matches the one that is
-        // triggering this callback.
-        if (renderTask === this.renderTask) {
-          this.renderTask = null;
-        }
-
-        if (((typeof PDFJSDev === 'undefined' ||
-              !PDFJSDev.test('PDFJS_NEXT')) && error === 'cancelled') ||
-            error instanceof RenderingCancelledException) {
-          renderCapability.resolve(undefined);
-          return;
-        }
-
-        this.renderingState = RenderingStates.FINISHED;
-        this._convertCanvasToImage();
-
-        if (!error) {
-          renderCapability.resolve(undefined);
-        } else {
-          renderCapability.reject(error);
-        }
-      };
-
-      let ctx = this._getPageDrawContext();
-      let drawViewport = this.viewport.clone({ scale: this.scale, });
-      let renderContinueCallback = (cont) => {
-        if (!this.renderingQueue.isHighestPriority(this)) {
-          this.renderingState = RenderingStates.PAUSED;
-          this.resume = () => {
-            this.renderingState = RenderingStates.RUNNING;
-            cont();
-          };
-          return;
-        }
-        cont();
-      };
-
-      let renderContext = {
-        canvasContext: ctx,
-        viewport: drawViewport,
-      };
-      let renderTask = this.renderTask = this.pdfPage.render(renderContext);
-      renderTask.onContinue = renderContinueCallback;
-
-      renderTask.promise.then(function() {
-        finishRenderTask(null);
-      }, function(error) {
-        finishRenderTask(error);
-      });
-      return renderCapability.promise;
-    },
+    this.div.setAttribute('data-loaded', true);
+    this.ring.appendChild(image);
 
-    setImage: function PDFThumbnailView_setImage(pageView) {
-      if (this.renderingState !== RenderingStates.INITIAL) {
-        return;
+    // Zeroing the width and height causes Firefox to release graphics
+    // resources immediately, which can greatly reduce memory consumption.
+    this.canvas.width = 0;
+    this.canvas.height = 0;
+    delete this.canvas;
+  }
+
+  draw() {
+    if (this.renderingState !== RenderingStates.INITIAL) {
+      console.error('Must be in new state before drawing');
+      return Promise.resolve(undefined);
+    }
+    this.renderingState = RenderingStates.RUNNING;
+
+    let renderCapability = createPromiseCapability();
+    let finishRenderTask = (error) => {
+      // The renderTask may have been replaced by a new one, so only remove
+      // the reference to the renderTask if it matches the one that is
+      // triggering this callback.
+      if (renderTask === this.renderTask) {
+        this.renderTask = null;
       }
-      var img = pageView.canvas;
-      if (!img) {
+
+      if (((typeof PDFJSDev === 'undefined' ||
+            !PDFJSDev.test('PDFJS_NEXT')) && error === 'cancelled') ||
+          error instanceof RenderingCancelledException) {
+        renderCapability.resolve(undefined);
         return;
       }
-      if (!this.pdfPage) {
-        this.setPdfPage(pageView.pdfPage);
-      }
 
       this.renderingState = RenderingStates.FINISHED;
+      this._convertCanvasToImage();
 
-      var ctx = this._getPageDrawContext(true);
-      var canvas = ctx.canvas;
+      if (!error) {
+        renderCapability.resolve(undefined);
+      } else {
+        renderCapability.reject(error);
+      }
+    };
 
-      if (img.width <= 2 * canvas.width) {
-        ctx.drawImage(img, 0, 0, img.width, img.height,
-                      0, 0, canvas.width, canvas.height);
-        this._convertCanvasToImage();
+    let ctx = this._getPageDrawContext();
+    let drawViewport = this.viewport.clone({ scale: this.scale, });
+    let renderContinueCallback = (cont) => {
+      if (!this.renderingQueue.isHighestPriority(this)) {
+        this.renderingState = RenderingStates.PAUSED;
+        this.resume = () => {
+          this.renderingState = RenderingStates.RUNNING;
+          cont();
+        };
         return;
       }
-      // drawImage does an awful job of rescaling the image, doing it gradually.
-      var MAX_NUM_SCALING_STEPS = 3;
-      var reducedWidth = canvas.width << MAX_NUM_SCALING_STEPS;
-      var reducedHeight = canvas.height << MAX_NUM_SCALING_STEPS;
-      var reducedImage = TempImageFactory.getCanvas(reducedWidth,
-                                                    reducedHeight);
-      var reducedImageCtx = reducedImage.getContext('2d');
-
-      while (reducedWidth > img.width || reducedHeight > img.height) {
-        reducedWidth >>= 1;
-        reducedHeight >>= 1;
-      }
-      reducedImageCtx.drawImage(img, 0, 0, img.width, img.height,
-                                0, 0, reducedWidth, reducedHeight);
-      while (reducedWidth > 2 * canvas.width) {
-        reducedImageCtx.drawImage(reducedImage,
-                                  0, 0, reducedWidth, reducedHeight,
-                                  0, 0, reducedWidth >> 1, reducedHeight >> 1);
-        reducedWidth >>= 1;
-        reducedHeight >>= 1;
-      }
-      ctx.drawImage(reducedImage, 0, 0, reducedWidth, reducedHeight,
+      cont();
+    };
+
+    let renderContext = {
+      canvasContext: ctx,
+      viewport: drawViewport,
+    };
+    let renderTask = this.renderTask = this.pdfPage.render(renderContext);
+    renderTask.onContinue = renderContinueCallback;
+
+    renderTask.promise.then(function() {
+      finishRenderTask(null);
+    }, function(error) {
+      finishRenderTask(error);
+    });
+    return renderCapability.promise;
+  }
+
+  setImage(pageView) {
+    if (this.renderingState !== RenderingStates.INITIAL) {
+      return;
+    }
+    let img = pageView.canvas;
+    if (!img) {
+      return;
+    }
+    if (!this.pdfPage) {
+      this.setPdfPage(pageView.pdfPage);
+    }
+
+    this.renderingState = RenderingStates.FINISHED;
+
+    let ctx = this._getPageDrawContext(true);
+    let canvas = ctx.canvas;
+    if (img.width <= 2 * canvas.width) {
+      ctx.drawImage(img, 0, 0, img.width, img.height,
                     0, 0, canvas.width, canvas.height);
       this._convertCanvasToImage();
-    },
+      return;
+    }
 
-    get pageId() {
-      return (this.pageLabel !== null ? this.pageLabel : this.id);
-    },
+    // drawImage does an awful job of rescaling the image, doing it gradually.
+    let reducedWidth = canvas.width << MAX_NUM_SCALING_STEPS;
+    let reducedHeight = canvas.height << MAX_NUM_SCALING_STEPS;
+    let reducedImage = TempImageFactory.getCanvas(reducedWidth,
+                                                  reducedHeight);
+    let reducedImageCtx = reducedImage.getContext('2d');
 
-    /**
-     * @param {string|null} label
-     */
-    setPageLabel: function PDFThumbnailView_setPageLabel(label) {
-      this.pageLabel = (typeof label === 'string' ? label : null);
+    while (reducedWidth > img.width || reducedHeight > img.height) {
+      reducedWidth >>= 1;
+      reducedHeight >>= 1;
+    }
+    reducedImageCtx.drawImage(img, 0, 0, img.width, img.height,
+                              0, 0, reducedWidth, reducedHeight);
+    while (reducedWidth > 2 * canvas.width) {
+      reducedImageCtx.drawImage(reducedImage,
+                                0, 0, reducedWidth, reducedHeight,
+                                0, 0, reducedWidth >> 1, reducedHeight >> 1);
+      reducedWidth >>= 1;
+      reducedHeight >>= 1;
+    }
+    ctx.drawImage(reducedImage, 0, 0, reducedWidth, reducedHeight,
+                  0, 0, canvas.width, canvas.height);
+    this._convertCanvasToImage();
+  }
 
-      this.l10n.get('thumb_page_title', { page: this.pageId, },
-                    'Page {{page}}').then((msg) => {
-        this.anchor.title = msg;
-      });
+  get pageId() {
+    return (this.pageLabel !== null ? this.pageLabel : this.id);
+  }
 
-      if (this.renderingState !== RenderingStates.FINISHED) {
-        return;
-      }
+  /**
+   * @param {string|null} label
+   */
+  setPageLabel(label) {
+    this.pageLabel = (typeof label === 'string' ? label : null);
 
-      this.l10n.get('thumb_page_canvas', { page: this.pageId, },
-                    'Thumbnail of Page {{page}}').then((ariaLabel) => {
-        if (this.image) {
-          this.image.setAttribute('aria-label', ariaLabel);
-        } else if (this.disableCanvasToImageConversion && this.canvas) {
-          this.canvas.setAttribute('aria-label', ariaLabel);
-        }
-      });
-    },
-  };
+    this.l10n.get('thumb_page_title', { page: this.pageId, },
+                  'Page {{page}}').then((msg) => {
+      this.anchor.title = msg;
+    });
 
-  PDFThumbnailView.cleanup = function() {
-    TempImageFactory.destroyCanvas();
-  };
+    if (this.renderingState !== RenderingStates.FINISHED) {
+      return;
+    }
 
-  return PDFThumbnailView;
-})();
+    this.l10n.get('thumb_page_canvas', { page: this.pageId, },
+                  'Thumbnail of Page {{page}}').then((ariaLabel) => {
+      if (this.image) {
+        this.image.setAttribute('aria-label', ariaLabel);
+      } else if (this.disableCanvasToImageConversion && this.canvas) {
+        this.canvas.setAttribute('aria-label', ariaLabel);
+      }
+    });
+  }
+
+  static cleanup() {
+    TempImageFactory.destroyCanvas();
+  }
+}
 
 export {
   PDFThumbnailView,