Use valueOf when converting String object values

lib/object.js

@@ -56,9 +56,9 @@ class PDFObject {
       // If so, encode it as big endian UTF-16
       let stringBuffer;
       if (isUnicode) {
-        stringBuffer = swapBytes(new Buffer(`\ufeff${string}`, 'utf16le'));
+        stringBuffer = swapBytes(Buffer.from(`\ufeff${string}`, 'utf16le'));
       } else {
-        stringBuffer = new Buffer(string, 'ascii');
+        stringBuffer = Buffer.from(string.valueOf(), 'ascii');
       }
 
       // Encrypt the string when necessary

tests/unit/object.spec.js

@@ -0,0 +1,23 @@
+const PDFObject = require('../../lib/object').default;
+
+describe('PDFObject', () => {
+  describe('convert', () => {
+    test('string literal', () => {
+      expect(PDFObject.convert('test')).toEqual('/test');
+    });
+
+    test('string literal with unicode', () => {
+      expect(PDFObject.convert('αβγδ')).toEqual('/αβγδ');
+    });
+
+    test('String object', () => {
+      expect(PDFObject.convert(new String('test'))).toEqual('(test)');
+    });
+
+    test('String object with unicode', () => {
+      const result = PDFObject.convert(new String('αβγδ'));
+      expect(result.length).toEqual(12);
+      expect(result).toMatchInlineSnapshot(`"(þÿ±²³´)"`);
+    });
+  });
+});