Add a getOrPutComputed method in the RefSetCache class

This is equivalent to the native `Map.prototype.getOrInsertComputed()` method, and it helps simplify/shorten some existing code.

src/core/editor/pdf_editor.js

@@ -455,12 +455,7 @@ class PDFEditor {
     // Re-entry means a (malformed) cycle back to this stream: allocate its
     // reference now to break the loop, like the generic path's eager alloc.
     if (resourceStreamPath.has(oldRef)) {
-      let ref = oldRefMapping.get(oldRef);
-      if (!ref) {
-        ref = this.newRef;
-        oldRefMapping.put(oldRef, ref);
-      }
-      return ref;
+      return oldRefMapping.getOrPutComputed(oldRef, () => this.newRef);
     }
 
     const key = oldRef.toString();

src/core/image_utils.js

@@ -228,11 +228,7 @@ class GlobalImageCache {
   }
 
   shouldCache(ref, pageIndex) {
-    let pageIndexSet = this._refCache.get(ref);
-    if (!pageIndexSet) {
-      pageIndexSet = new Set();
-      this._refCache.put(ref, pageIndexSet);
-    }
+    const pageIndexSet = this._refCache.getOrPutComputed(ref, () => new Set());
     pageIndexSet.add(pageIndex);
 
     if (pageIndexSet.size < GlobalImageCache.NUM_PAGES_THRESHOLD) {

src/core/primitives.js

@@ -398,6 +398,16 @@ class RefSetCache {
     this._map.set(ref.toString(), this.get(aliasRef));
   }
 
+  getOrPutComputed(ref, callback) {
+    const map = this._map,
+      refStr = ref.toString();
+
+    if (!map.has(refStr)) {
+      map.set(refStr, callback(ref));
+    }
+    return map.get(refStr);
+  }
+
   [Symbol.iterator]() {
     return this._map.values();
   }

src/core/struct_tree.js

@@ -93,12 +93,7 @@ class StructTreeRoot {
       return;
     }
     this.structParentIds ||= new RefSetCache();
-    let ids = this.structParentIds.get(pageRef);
-    if (!ids) {
-      ids = [];
-      this.structParentIds.put(pageRef, ids);
-    }
-    ids.push([id, type]);
+    this.structParentIds.getOrPutComputed(pageRef, makeArr).push([id, type]);
   }
 
   addAnnotationIdToPage(pageRef, id) {
@@ -537,11 +532,9 @@ class StructTreeRoot {
       return;
     }
 
-    let cachedParentDict = cache.get(parentRef);
-    if (!cachedParentDict) {
-      cachedParentDict = parentDict.clone();
-      cache.put(parentRef, cachedParentDict);
-    }
+    const cachedParentDict = cache.getOrPutComputed(parentRef, () =>
+      parentDict.clone()
+    );
     const parentKidsRaw = cachedParentDict.getRaw("K");
     let cachedParentKids =
       parentKidsRaw instanceof Ref ? cache.get(parentKidsRaw) : null;

test/unit/primitives_spec.js

@@ -568,6 +568,12 @@ describe("primitives", function () {
       cache.put(ref2, obj2);
       expect([...cache.keys()]).toEqual([ref1, ref2]);
     });
+
+    it("should handle getOrPutComputed correctly", function () {
+      expect(cache.getOrPutComputed(ref1, () => obj1)).toEqual(obj1);
+      // Trying to set it again should be ignored.
+      expect(cache.getOrPutComputed(ref1, () => obj2)).toEqual(obj1);
+    });
   });
 
   describe("isName", function () {