Convert the PageViewport to a proper ES6 class

Also converts all `var` to `let` for good measure.

src/display/dom_utils.js

@@ -137,13 +137,9 @@ class DOMSVGFactory {
 
 /**
  * PDF page viewport created based on scale, rotation and offset.
- * @class
- * @alias PageViewport
  */
-var PageViewport = (function PageViewportClosure() {
+class PageViewport {
   /**
-   * @constructor
-   * @private
    * @param viewBox {Array} xMin, yMin, xMax and yMax coordinates.
    * @param scale {number} scale of the viewport.
    * @param rotation {number} rotations of the viewport in degrees.
@@ -151,7 +147,7 @@ var PageViewport = (function PageViewportClosure() {
    * @param offsetY {number} offset Y
    * @param dontFlip {boolean} if true, axis Y will not be flipped.
    */
-  function PageViewport(viewBox, scale, rotation, offsetX, offsetY, dontFlip) {
+  constructor(viewBox, scale, rotation, offsetX, offsetY, dontFlip) {
     this.viewBox = viewBox;
     this.scale = scale;
     this.rotation = rotation;
@@ -160,9 +156,9 @@ var PageViewport = (function PageViewportClosure() {
 
     // creating transform to convert pdf coordinate system to the normal
     // canvas like coordinates taking in account scale and rotation
-    var centerX = (viewBox[2] + viewBox[0]) / 2;
+    let centerX = (viewBox[2] + viewBox[0]) / 2;
-    var centerY = (viewBox[3] + viewBox[1]) / 2;
+    let centerY = (viewBox[3] + viewBox[1]) / 2;
-    var rotateA, rotateB, rotateC, rotateD;
+    let rotateA, rotateB, rotateC, rotateD;
     rotation = rotation % 360;
     rotation = rotation < 0 ? rotation + 360 : rotation;
     switch (rotation) {
@@ -185,8 +181,8 @@ var PageViewport = (function PageViewportClosure() {
       rotateC = -rotateC; rotateD = -rotateD;
     }
 
-    var offsetCanvasX, offsetCanvasY;
+    let offsetCanvasX, offsetCanvasY;
-    var width, height;
+    let width, height;
     if (rotateA === 0) {
       offsetCanvasX = Math.abs(centerY - viewBox[1]) * scale + offsetX;
       offsetCanvasY = Math.abs(centerX - viewBox[0]) * scale + offsetY;
@@ -213,7 +209,7 @@ var PageViewport = (function PageViewportClosure() {
     this.width = width;
     this.height = height;
   }
-  PageViewport.prototype = /** @lends PageViewport.prototype */ {
+
   /**
    * Clones viewport with additional properties.
    * @param args {Object} (optional) If specified, may contain the 'scale' or
@@ -221,13 +217,14 @@ var PageViewport = (function PageViewportClosure() {
    * the cloned viewport.
    * @returns {PageViewport} Cloned viewport.
    */
-    clone: function PageViewPort_clone(args) {
+  clone(args) {
     args = args || {};
-      var scale = 'scale' in args ? args.scale : this.scale;
+    let scale = 'scale' in args ? args.scale : this.scale;
-      var rotation = 'rotation' in args ? args.rotation : this.rotation;
+    let rotation = 'rotation' in args ? args.rotation : this.rotation;
     return new PageViewport(this.viewBox.slice(), scale, rotation,
                             this.offsetX, this.offsetY, args.dontFlip);
-    },
+  }
+
   /**
    * Converts PDF point to the viewport coordinates. For examples, useful for
    * converting PDF location into canvas pixel coordinates.
@@ -238,9 +235,10 @@ var PageViewport = (function PageViewportClosure() {
    * @see {@link convertToPdfPoint}
    * @see {@link convertToViewportRectangle}
    */
-    convertToViewportPoint: function PageViewport_convertToViewportPoint(x, y) {
+  convertToViewportPoint(x, y) {
     return Util.applyTransform([x, y], this.transform);
-    },
+  }
+
   /**
    * Converts PDF rectangle to the viewport coordinates.
    * @param rect {Array} xMin, yMin, xMax and yMax coordinates.
@@ -248,12 +246,12 @@ var PageViewport = (function PageViewportClosure() {
    * in the viewport coordinate space.
    * @see {@link convertToViewportPoint}
    */
-    convertToViewportRectangle:
+  convertToViewportRectangle(rect) {
-      function PageViewport_convertToViewportRectangle(rect) {
+    let tl = Util.applyTransform([rect[0], rect[1]], this.transform);
-      var tl = Util.applyTransform([rect[0], rect[1]], this.transform);
+    let br = Util.applyTransform([rect[2], rect[3]], this.transform);
-      var br = Util.applyTransform([rect[2], rect[3]], this.transform);
     return [tl[0], tl[1], br[0], br[1]];
-    },
+  }
+
   /**
    * Converts viewport coordinates to the PDF location. For examples, useful
    * for converting canvas pixel location into PDF one.
@@ -263,12 +261,10 @@ var PageViewport = (function PageViewportClosure() {
    * point in the PDF coordinate space.
    * @see {@link convertToViewportPoint}
    */
-    convertToPdfPoint: function PageViewport_convertToPdfPoint(x, y) {
+  convertToPdfPoint(x, y) {
     return Util.applyInverseTransform([x, y], this.transform);
-    },
+  }
-  };
+}
-  return PageViewport;
-})();
 
 var RenderingCancelledException = (function RenderingCancelledException() {
   function RenderingCancelledException(msg, type) {