fix: fix marked.use with multiple args (#2651)

Fixes undefined

src/marked.js

@@ -153,20 +153,23 @@ marked.defaults = defaults;
  */
 
 marked.use = function(...args) {
-  const opts = merge({}, ...args);
   const extensions = marked.defaults.extensions || { renderers: {}, childTokens: {} };
-  let hasExtensions;
 
   args.forEach((pack) => {
+    // copy options to new object
+    const opts = merge({}, pack);
+
+    // set async to true if it was set to true before
+    opts.async = marked.defaults.async || opts.async;
+
     // ==-- Parse "addon" extensions --== //
     if (pack.extensions) {
-      hasExtensions = true;
       pack.extensions.forEach((ext) => {
         if (!ext.name) {
           throw new Error('extension name required');
         }
         if (ext.renderer) { // Renderer extensions
-          const prevRenderer = extensions.renderers ? extensions.renderers[ext.name] : null;
+          const prevRenderer = extensions.renderers[ext.name];
           if (prevRenderer) {
             // Replace extension with func to run new extension but fall back if false
             extensions.renderers[ext.name] = function(...args) {
@@ -209,6 +212,7 @@ marked.use = function(...args) {
           extensions.childTokens[ext.name] = ext.childTokens;
         }
       });
+      opts.extensions = extensions;
     }
 
     // ==-- Parse "overwrite" extensions --== //
@@ -256,10 +260,6 @@ marked.use = function(...args) {
       };
     }
 
-    if (hasExtensions) {
-      opts.extensions = extensions;
-    }
-
     marked.setOptions(opts);
   });
 };

test/unit/marked-spec.js

@@ -1,4 +1,4 @@
-import { marked, Renderer, Slugger, lexer, parseInline, use, getDefaults, walkTokens as _walkTokens } from '../../src/marked.js';
+import { marked, Renderer, Slugger, lexer, parseInline, use, getDefaults, walkTokens as _walkTokens, defaults, setOptions } from '../../src/marked.js';
 
 describe('Test heading ID functionality', () => {
   it('should add id attribute by default', () => {
@@ -612,6 +612,41 @@ used extension2 walked</p>
 
       runTest();
     });
+
+    it('should merge extensions correctly', () => {
+      use(
+        {},
+        { tokenizer: {} },
+        { renderer: {} },
+        { walkTokens: () => {} },
+        { extensions: [] }
+      );
+
+      expect(() => marked('# test')).not.toThrow();
+    });
+  });
+
+  it('should be async if any extension in use args is async', () => {
+    use(
+      { async: true },
+      { async: false }
+    );
+
+    expect(defaults.async).toBeTrue();
+  });
+
+  it('should be async if any extension in use is async', () => {
+    use({ async: true });
+    use({ async: false });
+
+    expect(defaults.async).toBeTrue();
+  });
+
+  it('should reset async with setOptions', () => {
+    use({ async: true });
+    setOptions({ async: false });
+
+    expect(defaults.async).toBeFalse();
   });
 
   it('should allow deleting/editing tokens', () => {