fix: stop bare addPage() from re-forcing the document's default font

lib/page.js

@@ -85,8 +85,21 @@ class PDFPage {
 
     this.content = this.document.ref();
 
-    if (options.font) document.font(options.font, options.fontFamily);
-    if (options.fontSize) document.fontSize(options.fontSize);
+    // `options` defaults to `document.options` (the PDFDocument constructor options) when
+    // addPage() is called without arguments, so it's the same object for every page. Applying
+    // font/fontSize from it unconditionally would silently override any doc.font()/doc.fontSize()
+    // call made since the previous page. Only (re-)apply them here when they were explicitly
+    // passed to this addPage() call, or for the very first page (document.page is still null),
+    // where they're the intended initial default - already applied by initFonts(), so this is
+    // just keeping fontSize/margin calculation below consistent.
+    const isInheritedDefaultOptions = options === document.options;
+    const isFirstPage = document.page == null;
+    if (options.font && (!isInheritedDefaultOptions || isFirstPage)) {
+      document.font(options.font, options.fontFamily);
+    }
+    if (options.fontSize && (!isInheritedDefaultOptions || isFirstPage)) {
+      document.fontSize(options.fontSize);
+    }
 
     // process margins
     // Margin calculation must occur after font assignment to ensure any dynamic sizes are calculated correctly

tests/unit/page.spec.js

@@ -28,4 +28,34 @@ describe('page', function () {
       expect(page.margins).toEqual({ top: 0, right: 0, bottom: 0, left: 0 });
     });
   });
+
+  // https://github.com/foliojs/pdfkit/issues/1739
+  describe('font persistence across addPage()', function () {
+    test('a font set with doc.font() persists onto a bare addPage() call', function () {
+      const doc = new PDFDocument({ font: 'Helvetica' });
+      doc.font('Helvetica-Bold');
+      doc.addPage();
+      expect(doc._font.name).toBe('Helvetica-Bold');
+    });
+
+    test('a font size set with doc.fontSize() persists onto a bare addPage() call', function () {
+      const doc = new PDFDocument({ font: 'Helvetica' });
+      doc.fontSize(30);
+      doc.addPage();
+      expect(doc._fontSize).toBe(30);
+    });
+
+    test('an explicit font passed to addPage() still overrides the current font', function () {
+      const doc = new PDFDocument({ font: 'Helvetica' });
+      doc.font('Helvetica-Bold');
+      doc.addPage({ font: 'Times-Roman' });
+      expect(doc._font.name).toBe('Times-Roman');
+    });
+
+    test('an explicit fontSize passed to addPage() still applies', function () {
+      const doc = new PDFDocument({ font: 'Helvetica' });
+      doc.addPage({ fontSize: 20 });
+      expect(doc._fontSize).toBe(20);
+    });
+  });
 });