feat: Add serializeOuter method

Fixes inikulin#230, inikulin#378

Uses the test case from inikulin#378, by @joeldenning

Co-Authored-By: Joel Denning <5524384+joeldenning@users.noreply.github.com>

packages/parse5/lib/index.ts

@@ -4,7 +4,7 @@ import type { DefaultTreeAdapterMap } from './tree-adapters/default.js';
 import type { TreeAdapterTypeMap } from './tree-adapters/interface.js';
 
 export { ParserOptions } from './parser/index.js';
-export { serialize, SerializerOptions } from './serializer/index.js';
+export { serialize, serializeOuter, SerializerOptions } from './serializer/index.js';
 
 // Shorthands
 

packages/parse5/lib/serializer/index.test.ts

@@ -3,7 +3,7 @@ import * as parse5 from 'parse5';
 import outdent from 'outdent';
 import { generateSerializerTests } from 'parse5-test-utils/utils/generate-serializer-tests.js';
 import { treeAdapters } from 'parse5-test-utils/utils/common.js';
-import type { Element } from 'parse5/dist/tree-adapters/default';
+import { type Element, isElementNode } from 'parse5/dist/tree-adapters/default';
 
 generateSerializerTests('serializer', 'Serializer', parse5.serialize);
 
@@ -49,4 +49,15 @@ describe('serializer', () => {
             expect(parse5.serialize(document)).toContain(input);
         });
     });
+
+    describe('serializeOuter', () => {
+        it('serializes outerHTML correctly', () => {
+            const document = parse5.parseFragment('<div><button>Hello</button></div>');
+            const div = document.childNodes[0];
+            assert.ok(isElementNode(div));
+            const html = parse5.serializeOuter(div);
+
+            assert.equal(html, '<div><button>Hello</button></div>');
+        });
+    });
 });

packages/parse5/lib/serializer/index.ts

@@ -50,6 +50,8 @@ export interface SerializerOptions<T extends TreeAdapterTypeMap> {
 
 type InternalOptions<T extends TreeAdapterTypeMap> = Required<SerializerOptions<T>>;
 
+const defaultOpts = { treeAdapter: DefaultTreeAdapter, scriptingEnabled: true };
+
 /**
  * Serializes an AST node to an HTML string.
  *
@@ -76,10 +78,37 @@ export function serialize<T extends TreeAdapterTypeMap = DefaultTreeAdapter.Defa
     node: T['parentNode'],
     options?: SerializerOptions<T>
 ): string {
-    const opts = { treeAdapter: DefaultTreeAdapter, scriptingEnabled: true, ...options };
+    const opts = { ...defaultOpts, ...options };
     return serializeChildNodes(node, opts);
 }
 
+/**
+ * Serializes an AST element node to an HTML string, including the element node.
+ *
+ * @example
+ *
+ * ```js
+ * const parse5 = require('parse5');
+ *
+ * const document = parse5.parseFragment('<div>Hello, <b>world</b>!</div>');
+ *
+ * // Serializes the <div> element.
+ * const html = parse5.serializeOuter(document.childNodes[0]);
+ *
+ * console.log(str); //> '<div>Hello, <b>world</b>!</div>'
+ * ```
+ *
+ * @param node Node to serialize.
+ * @param options Serialization options.
+ */
+export function serializeOuter<T extends TreeAdapterTypeMap = DefaultTreeAdapter.DefaultTreeAdapterMap>(
+    node: T['element'],
+    options?: SerializerOptions<T>
+): string {
+    const opts = { ...defaultOpts, ...options };
+    return serializeElement(node, opts);
+}
+
 function serializeChildNodes<T extends TreeAdapterTypeMap>(
     parentNode: T['parentNode'],
     options: InternalOptions<T>