Reduce the overall indentation level in `Catalog_readDocumentOutline`, by using early returns, in order to improve readability

src/core/obj.js

@@ -128,26 +128,29 @@ var Catalog = (function CatalogClosure() {
       return shadow(this, 'documentOutline', obj);
     },
     readDocumentOutline: function Catalog_readDocumentOutline() {
-      var xref = this.xref;
       var obj = this.catDict.get('Outlines');
-      var root = { items: [] };
-      if (isDict(obj)) {
+      if (!isDict(obj)) {
+        return null;
+      }
       obj = obj.getRaw('First');
-        var processed = new RefSet();
-        if (isRef(obj)) {
+      if (!isRef(obj)) {
+        return null;
+      }
+      var root = { items: [] };
       var queue = [{obj: obj, parent: root}];
-          // to avoid recursion keeping track of the items
-          // in the processed dictionary
+      // To avoid recursion, keep track of the already processed items.
+      var processed = new RefSet();
       processed.put(obj);
+      var xref = this.xref;
+
       while (queue.length > 0) {
         var i = queue.shift();
         var outlineDict = xref.fetchIfRef(i.obj);
         if (outlineDict === null) {
           continue;
         }
-            if (!outlineDict.has('Title')) {
-              error('Invalid outline item');
-            }
+        assert(outlineDict.has('Title'), 'Invalid outline item');
+
         var actionDict = outlineDict.get('A'), dest = null, url = null;
         if (actionDict) {
           var destEntry = actionDict.get('D');
@@ -188,8 +191,6 @@ var Catalog = (function CatalogClosure() {
           processed.put(obj);
         }
       }
-        }
-      }
       return (root.items.length > 0 ? root.items : null);
     },
     get numPages() {

test/unit/api_spec.js

@@ -430,6 +430,19 @@ describe('api', function() {
         loadingTask.destroy();
       });
     });
+    it('gets non-existent outline', function() {
+      var url = combineUrl(window.location.href, '../pdfs/tracemonkey.pdf');
+      var loadingTask = PDFJS.getDocument(url);
+
+      var promise = loadingTask.promise.then(function (pdfDocument) {
+        return pdfDocument.getOutline();
+      });
+      waitsForPromiseResolved(promise, function (outline) {
+        expect(outline).toEqual(null);
+
+        loadingTask.destroy();
+      });
+    });
     it('gets outline', function() {
       var promise = doc.getOutline();
       waitsForPromiseResolved(promise, function(outline) {