src/core/annotation.js

@@ -3488,8 +3488,8 @@ class ChoiceWidgetAnnotation extends WidgetAnnotation {
       // always make the field value an array with zero, one or multiple items.
       if (typeof this.data.fieldValue === "string") {
         this.data.fieldValue = [this.data.fieldValue];
-      } else {
+      } else if (!this.data.fieldValue) {
-        this.data.fieldValue ||= [];
+        this.data.fieldValue = [];
       }
     } else {
       // The specs say that we should have an indices array only with

src/core/catalog.js

@@ -998,7 +998,9 @@ class Catalog {
         warn(`Bad value, for key "${key}", in ViewerPreferences: ${value}.`);
         continue;
       }
-      prefs ??= Object.create(null);
+      if (!prefs) {
+        prefs = Object.create(null);
+      }
       prefs[key] = prefValue;
     }
     return shadow(this, "viewerPreferences", prefs);
@@ -1040,7 +1042,9 @@ class Catalog {
       const nameTree = new NameTree(obj.getRaw("EmbeddedFiles"), this.xref);
       for (const [key, value] of nameTree.getAll()) {
         const fs = new FileSpec(value, this.xref);
-        attachments ??= Object.create(null);
+        if (!attachments) {
+          attachments = Object.create(null);
+        }
         attachments[stringToPDFString(key)] = fs.serializable;
       }
     }
@@ -1054,7 +1058,9 @@ class Catalog {
     if (obj instanceof Dict && obj.has("XFAImages")) {
       const nameTree = new NameTree(obj.getRaw("XFAImages"), this.xref);
       for (const [key, value] of nameTree.getAll()) {
-        xfaImages ??= new Dict(this.xref);
+        if (!xfaImages) {
+          xfaImages = new Dict(this.xref);
+        }
         xfaImages.set(stringToPDFString(key), value);
       }
     }

src/core/document.js

@@ -1532,7 +1532,9 @@ class PDFDocument {
             warn(`Bad value, for custom key "${key}", in Info: ${value}.`);
             continue;
           }
-          docInfo.Custom ??= Object.create(null);
+          if (!docInfo.Custom) {
+            docInfo.Custom = Object.create(null);
+          }
           docInfo.Custom[key] = customValue;
           continue;
       }

src/core/xfa/parser.js

@@ -91,7 +91,9 @@ class XFAParser extends XMLParserBase {
         }
       } else if (name.startsWith("xmlns:")) {
         const prefix = name.substring("xmlns:".length);
-        prefixes ??= [];
+        if (!prefixes) {
+          prefixes = [];
+        }
         prefixes.push({ prefix, value });
       } else {
         const i = name.indexOf(":");
@@ -100,7 +102,10 @@ class XFAParser extends XMLParserBase {
         } else {
           // Attributes can have their own namespace.
           // For example in data, we can have <foo xfa:dataNode="dataGroup"/>
-          const nsAttrs = (attributeObj[$nsAttributes] ??= Object.create(null));
+          let nsAttrs = attributeObj[$nsAttributes];
+          if (!nsAttrs) {
+            nsAttrs = attributeObj[$nsAttributes] = Object.create(null);
+          }
           const [ns, attrName] = [name.slice(0, i), name.slice(i + 1)];
           const attrs = (nsAttrs[ns] ||= Object.create(null));
           attrs[attrName] = value;

src/core/xfa/template.js

@@ -2462,7 +2462,9 @@ class ExclGroup extends XFAObject {
 
     setAccess(this, attributes.class);
 
-    this[$extra] ||= Object.create(null);
+    if (!this[$extra]) {
+      this[$extra] = Object.create(null);
+    }
 
     Object.assign(this[$extra], {
       children,
@@ -2951,7 +2953,9 @@ class Field extends XFAObject {
       }
     }
 
-    ui.attributes.style ||= Object.create(null);
+    if (!ui.attributes.style) {
+      ui.attributes.style = Object.create(null);
+    }
 
     let aElement = null;
 
@@ -3044,7 +3048,9 @@ class Field extends XFAObject {
       caption.attributes.class[0] = "xfaCaptionForCheckButton";
     }
 
-    ui.attributes.class ||= [];
+    if (!ui.attributes.class) {
+      ui.attributes.class = [];
+    }
 
     ui.children.splice(0, 0, caption);
 
@@ -4061,9 +4067,11 @@ class PageArea extends XFAObject {
   }
 
   [$getNextPage]() {
-    this[$extra] ||= {
+    if (!this[$extra]) {
-      numberOfUse: 0,
+      this[$extra] = {
-    };
+        numberOfUse: 0,
+      };
+    }
 
     const parent = this[$getParent]();
     if (parent.relation === "orderedOccurrence") {
@@ -4082,9 +4090,11 @@ class PageArea extends XFAObject {
 
   [$toHTML]() {
     // TODO: incomplete.
-    this[$extra] ||= {
+    if (!this[$extra]) {
-      numberOfUse: 1,
+      this[$extra] = {
-    };
+        numberOfUse: 1,
+      };
+    }
 
     const children = [];
     this[$extra].children = children;
@@ -4176,11 +4186,13 @@ class PageSet extends XFAObject {
   }
 
   [$getNextPage]() {
-    this[$extra] ||= {
+    if (!this[$extra]) {
-      numberOfUse: 1,
+      this[$extra] = {
-      pageIndex: -1,
+        numberOfUse: 1,
-      pageSetIndex: -1,
+        pageIndex: -1,
-    };
+        pageSetIndex: -1,
+      };
+    }
 
     if (this.relation === "orderedOccurrence") {
       if (this[$extra].pageIndex + 1 < this.pageArea.children.length) {
@@ -5055,7 +5067,9 @@ class Subform extends XFAObject {
 
     setAccess(this, attributes.class);
 
-    this[$extra] ||= Object.create(null);
+    if (!this[$extra]) {
+      this[$extra] = Object.create(null);
+    }
 
     Object.assign(this[$extra], {
       children,
@@ -5481,7 +5495,9 @@ class Template extends XFAObject {
       }
     }
 
-    pageArea ||= pageAreas[0];
+    if (!pageArea) {
+      pageArea = pageAreas[0];
+    }
 
     pageArea[$extra] = {
       numberOfUse: 1,

src/scripting_api/app.js

@@ -202,15 +202,18 @@ class App extends PDFObject {
   }
 
   get constants() {
-    return (this._constants ??= Object.freeze({
+    if (!this._constants) {
-      align: Object.freeze({
+      this._constants = Object.freeze({
-        left: 0,
+        align: Object.freeze({
-        center: 1,
+          left: 0,
-        right: 2,
+          center: 1,
-        top: 3,
+          right: 2,
-        bottom: 4,
+          top: 3,
-      }),
+          bottom: 4,
-    }));
+        }),
+      });
+    }
+    return this._constants;
   }
 
   set constants(_) {