Remove the RefSet primitive

It's only used in `src/core/obj.js` in a handful of places where
nowadays a regular JavaScript set works too (the `RefSet` primitive
predates the usage of ES6). Not only are built-in data structures
often more efficient/optimized, it also avoids having to maintain a
custom data structure.

Previously, each call to a `RefSet` method would cause `toString` to be
called on the given `Ref`. As an additional bonus, using a regular
JavaScript set allows us to limit the number of times `toString` is
called now, simply by calling it once for `has` and `add` calls, for
example. Therefore, this is also more efficient since it avoids the
creation of intermediate strings.

src/core/obj.js

@@ -42,7 +42,6 @@ import {
   isRefsEqual,
   isStream,
   Ref,
-  RefSet,
   RefSetCache,
 } from "./primitives.js";
 import { Lexer, Parser } from "./parser.js";
@@ -148,8 +147,8 @@ class Catalog {
     const root = { items: [] };
     const queue = [{ obj, parent: root }];
     // To avoid recursion, keep track of the already processed items.
-    const processed = new RefSet();
-    processed.put(obj);
+    const processed = new Set();
+    processed.add(obj.toString());
     const xref = this.xref,
       blackColor = new Uint8ClampedArray(3);
 
@@ -199,14 +198,20 @@ class Catalog {
 
       i.parent.items.push(outlineItem);
       obj = outlineDict.getRaw("First");
-      if (isRef(obj) && !processed.has(obj)) {
-        queue.push({ obj, parent: outlineItem });
-        processed.put(obj);
+      if (isRef(obj)) {
+        const objString = obj.toString();
+        if (!processed.has(objString)) {
+          queue.push({ obj, parent: outlineItem });
+          processed.add(objString);
+        }
       }
       obj = outlineDict.getRaw("Next");
-      if (isRef(obj) && !processed.has(obj)) {
-        queue.push({ obj, parent: i.parent });
-        processed.put(obj);
+      if (isRef(obj)) {
+        const objString = obj.toString();
+        if (!processed.has(objString)) {
+          queue.push({ obj, parent: i.parent });
+          processed.add(objString);
+        }
       }
     }
     return root.items.length > 0 ? root.items : null;
@@ -738,7 +743,7 @@ class Catalog {
   getPageDict(pageIndex) {
     const capability = createPromiseCapability();
     const nodesToVisit = [this.catDict.getRaw("Pages")];
-    const visitedNodes = new RefSet();
+    const visitedNodes = new Set();
     const xref = this.xref,
       pageKidsCountCache = this.pageKidsCountCache;
     let count,
@@ -756,13 +761,14 @@ class Catalog {
             continue;
           }
           // Prevent circular references in the /Pages tree.
-          if (visitedNodes.has(currentNode)) {
+          const currentNodeStr = currentNode.toString();
+          if (visitedNodes.has(currentNodeStr)) {
             capability.reject(
               new FormatError("Pages tree contains circular reference.")
             );
             return;
           }
-          visitedNodes.put(currentNode);
+          visitedNodes.add(currentNodeStr);
 
           xref.fetchAsync(currentNode).then(function (obj) {
             if (isDict(obj, "Page") || (isDict(obj) && !obj.has("Kids"))) {
@@ -1962,8 +1968,8 @@ class NameOrNumberTree {
     }
     const xref = this.xref;
     // Reading Name/Number tree.
-    const processed = new RefSet();
-    processed.put(this.root);
+    const processed = new Set();
+    processed.add(this.root.toString());
     const queue = [this.root];
     while (queue.length > 0) {
       const obj = xref.fetchIfRef(queue.shift());
@@ -1974,11 +1980,12 @@ class NameOrNumberTree {
         const kids = obj.get("Kids");
         for (let i = 0, ii = kids.length; i < ii; i++) {
           const kid = kids[i];
-          if (processed.has(kid)) {
+          const kidStr = kid.toString();
+          if (processed.has(kidStr)) {
             throw new FormatError(`Duplicate entry in "${this._type}" tree.`);
           }
           queue.push(kid);
-          processed.put(kid);
+          processed.add(kidStr);
         }
         continue;
       }
@@ -2244,7 +2251,7 @@ const ObjectLoader = (function () {
       }
 
       const { keys, dict } = this;
-      this.refSet = new RefSet();
+      this.refSet = new Set();
       // Setup the initial nodes to visit.
       const nodesToVisit = [];
       for (let i = 0, ii = keys.length; i < ii; i++) {
@@ -2267,11 +2274,12 @@ const ObjectLoader = (function () {
         // Only references or chunked streams can cause missing data exceptions.
         if (currentNode instanceof Ref) {
           // Skip nodes that have already been visited.
-          if (this.refSet.has(currentNode)) {
+          const currentNodeStr = currentNode.toString();
+          if (this.refSet.has(currentNodeStr)) {
             continue;
           }
           try {
-            this.refSet.put(currentNode);
+            this.refSet.add(currentNodeStr);
             currentNode = this.xref.fetch(currentNode);
           } catch (ex) {
             if (!(ex instanceof MissingDataException)) {
@@ -2307,7 +2315,7 @@ const ObjectLoader = (function () {
           // Remove any reference nodes from the current `RefSet` so they
           // aren't skipped when we revist them.
           if (node instanceof Ref) {
-            this.refSet.remove(node);
+            this.refSet.delete(node.toString());
           }
         }
         return this._walk(nodesToRevisit);

src/core/primitives.js

@@ -219,31 +219,6 @@ var Ref = (function RefClosure() {
   return Ref;
 })();
 
-// The reference is identified by number and generation.
-// This structure stores only one instance of the reference.
-var RefSet = (function RefSetClosure() {
-  // eslint-disable-next-line no-shadow
-  function RefSet() {
-    this.dict = Object.create(null);
-  }
-
-  RefSet.prototype = {
-    has: function RefSet_has(ref) {
-      return ref.toString() in this.dict;
-    },
-
-    put: function RefSet_put(ref) {
-      this.dict[ref.toString()] = true;
-    },
-
-    remove: function RefSet_remove(ref) {
-      delete this.dict[ref.toString()];
-    },
-  };
-
-  return RefSet;
-})();
-
 var RefSetCache = (function RefSetCacheClosure() {
   // eslint-disable-next-line no-shadow
   function RefSetCache() {
@@ -337,7 +312,6 @@ export {
   Dict,
   Name,
   Ref,
-  RefSet,
   RefSetCache,
   isEOF,
   isCmd,

test/unit/primitives_spec.js

@@ -23,7 +23,6 @@ import {
   isRefsEqual,
   Name,
   Ref,
-  RefSet,
 } from "../../src/core/primitives.js";
 import { XRefMock } from "./test_utils.js";
 
@@ -285,24 +284,6 @@ describe("primitives", function () {
     });
   });
 
-  describe("RefSet", function () {
-    it("should have a stored value", function () {
-      var ref = Ref.get(4, 2);
-      var refset = new RefSet();
-      refset.put(ref);
-      expect(refset.has(ref)).toBeTruthy();
-    });
-    it("should not have an unknown value", function () {
-      var ref = Ref.get(4, 2);
-      var refset = new RefSet();
-      expect(refset.has(ref)).toBeFalsy();
-
-      refset.put(ref);
-      var anotherRef = Ref.get(2, 4);
-      expect(refset.has(anotherRef)).toBeFalsy();
-    });
-  });
-
   describe("isName", function () {
     it("handles non-names", function () {
       var nonName = {};