fix: support SSR environments where Element is not defined (#251) (#252)

The `draggableOpts.offsetParent` prop type used `PropTypes.instanceOf(Element)`
which throws a ReferenceError in SSR/Node.js environments where the DOM global
`Element` doesn't exist.

This was introduced in a prior release that added the draggableOpts prop type
definitions. The fix checks if Element is defined before using instanceOf.

Author: STRML

__tests__/ssr.test.js

@@ -0,0 +1,34 @@
+/**
+ * @jest-environment node
+ */
+// #251 - Test SSR compatibility where Element is not defined
+
+describe('SSR compatibility', () => {
+  test('propTypes.js can be imported in Node.js environment without Element global', () => {
+    // In Node.js environment (jest-environment: node), Element is not defined
+    expect(typeof Element).toBe('undefined');
+
+    // This should not throw ReferenceError: Element is not defined
+    expect(() => {
+      require('../lib/propTypes');
+    }).not.toThrow();
+  });
+
+  test('Resizable.js can be imported in Node.js environment without Element global', () => {
+    expect(typeof Element).toBe('undefined');
+
+    // This should not throw ReferenceError: Element is not defined
+    expect(() => {
+      require('../lib/Resizable');
+    }).not.toThrow();
+  });
+
+  test('ResizableBox.js can be imported in Node.js environment without Element global', () => {
+    expect(typeof Element).toBe('undefined');
+
+    // This should not throw ReferenceError: Element is not defined
+    expect(() => {
+      require('../lib/ResizableBox');
+    }).not.toThrow();
+  });
+});

lib/propTypes.js

@@ -76,7 +76,8 @@ export const resizableProps: Object = {
     children: PropTypes.node,
     disabled: PropTypes.bool,
     enableUserSelectHack: PropTypes.bool,
-    offsetParent: PropTypes.instanceOf(Element),
+    // #251: Check for Element to support SSR environments where DOM globals don't exist
+    offsetParent: typeof Element !== 'undefined' ? PropTypes.instanceOf(Element) : PropTypes.any,
     grid: PropTypes.arrayOf(PropTypes.number),
     handle: PropTypes.string,
     nodeRef: PropTypes.object,