fix(html): prevent tsdown from stripping custom element registrations (#703)

packages/html/src/define/tests/safe-define.test.ts

@@ -0,0 +1,36 @@
+import { describe, expect, it } from 'vitest';
+import { safeDefine } from '../safe-define';
+
+describe('safeDefine', () => {
+  it('registers a custom element', () => {
+    class TestElement extends HTMLElement {
+      static tagName = 'test-sd-register';
+    }
+
+    expect(customElements.get('test-sd-register')).toBeUndefined();
+    safeDefine(TestElement);
+    expect(customElements.get('test-sd-register')).toBe(TestElement);
+  });
+
+  it('does not throw when element is already registered', () => {
+    class TestElement extends HTMLElement {
+      static tagName = 'test-sd-no-throw';
+    }
+
+    customElements.define('test-sd-no-throw', TestElement);
+    expect(() => safeDefine(TestElement)).not.toThrow();
+  });
+
+  it('does not replace an existing registration', () => {
+    class Original extends HTMLElement {
+      static tagName = 'test-sd-no-replace';
+    }
+    class Replacement extends HTMLElement {
+      static tagName = 'test-sd-no-replace';
+    }
+
+    safeDefine(Original);
+    safeDefine(Replacement);
+    expect(customElements.get('test-sd-no-replace')).toBe(Original);
+  });
+});