Convert Catalog.getPageDict to an async method

This makes it possible to remove the internal `next` helper function, and also gets rid of the need to manually resolve/reject a `PromiseCapability`.

src/core/obj.js

@@ -14,10 +14,9 @@
  */
 
 import {
-  assert, bytesToString, createPromiseCapability, createValidAbsoluteUrl,
+  assert, bytesToString, createValidAbsoluteUrl, FormatError, info,
-  FormatError, info, InvalidPDFException, isBool, isNum, isString,
+  InvalidPDFException, isBool, isNum, isString, PermissionFlag, shadow,
-  PermissionFlag, shadow, stringToPDFString, stringToUTF8String, unreachable,
+  stringToPDFString, stringToUTF8String, unreachable, warn
-  warn
 } from '../shared/util';
 import {
   clearPrimitiveCaches, Cmd, Dict, isCmd, isDict, isName, isRef, isRefsEqual,
@@ -680,13 +679,11 @@ class Catalog {
     });
   }
 
-  getPageDict(pageIndex) {
+  async getPageDict(pageIndex) {
-    const capability = createPromiseCapability();
     const nodesToVisit = [this.catDict.getRaw('Pages')];
     const xref = this.xref, pageKidsCountCache = this.pageKidsCountCache;
     let count, currentPageIndex = 0;
 
-    function next() {
     while (nodesToVisit.length) {
       const currentNode = nodesToVisit.pop();
 
@@ -697,8 +694,8 @@ class Catalog {
           currentPageIndex += count;
           continue;
         }
+        const obj = await xref.fetchAsync(currentNode);
 
-          xref.fetchAsync(currentNode).then(function(obj) {
         if (isDict(obj, 'Page') || (isDict(obj) && !obj.has('Kids'))) {
           if (pageIndex === currentPageIndex) {
             // Cache the Page reference, since it can *greatly* improve
@@ -707,24 +704,19 @@ class Catalog {
             if (currentNode && !pageKidsCountCache.has(currentNode)) {
               pageKidsCountCache.put(currentNode, 1);
             }
-                capability.resolve([obj, currentNode]);
+            return [obj, currentNode];
-              } else {
-                currentPageIndex++;
-                next();
           }
-              return;
+          currentPageIndex++;
+          continue;
         }
         nodesToVisit.push(obj);
-            next();
+        continue;
-          }, capability.reject);
-          return;
       }
 
       // Must be a child page dictionary.
       if (!isDict(currentNode)) {
-          capability.reject(new FormatError(
+        throw new FormatError(
-            'Page dictionary kid reference points to wrong type of object.'));
+          'Page dictionary kid reference points to wrong type of object.');
-          return;
       }
 
       count = currentNode.get('Count');
@@ -750,16 +742,12 @@ class Catalog {
         if (isName(currentNode.get('Type'), 'Page') ||
             (!currentNode.has('Type') && currentNode.has('Contents'))) {
           if (currentPageIndex === pageIndex) {
-              capability.resolve([currentNode, null]);
+            return [currentNode, null];
-              return;
           }
           currentPageIndex++;
           continue;
         }
-
+        throw new FormatError('Page dictionary kids object is not an array.');
-          capability.reject(new FormatError(
-            'Page dictionary kids object is not an array.'));
-          return;
       }
 
       // Always check all `Kids` nodes, to avoid getting stuck in an empty
@@ -769,10 +757,7 @@ class Catalog {
         nodesToVisit.push(kids[last]);
       }
     }
-      capability.reject(new Error(`Page index ${pageIndex} not found.`));
+    throw new Error(`Page index ${pageIndex} not found.`);
-    }
-    next();
-    return capability.promise;
   }
 
   getPageIndex(pageRef) {