feat: support TransitionEvent init properties

src/__tests__/events.js

@@ -358,6 +358,22 @@ test('assigns clipboardData properties', () => {
   expect(clipboardData.getData('text')).toBe('example')
 })
 
+test('assigns TransitionEvent init properties', () => {
+  const node = document.createElement('div')
+  const spy = jest.fn()
+  node.addEventListener('transitionend', spy)
+  const transitionEventInit = {
+    propertyName: 'opacity',
+    elapsedTime: 100,
+    pseudoElement: '',
+  }
+  fireEvent.transitionEnd(node, transitionEventInit)
+  expect(spy).toHaveBeenCalledTimes(1)
+  expect(spy.mock.calls[0][0]).toEqual(
+    expect.objectContaining(transitionEventInit),
+  )
+})
+
 test('fires events on Window', () => {
   const messageSpy = jest.fn()
   window.addEventListener('message', messageSpy)

src/events.js

@@ -62,6 +62,23 @@ function createEvent(
     })
   }
 
+  // TransitionEvent is not supported in jsdom: https://github.com/jsdom/jsdom/issues/1781
+  if (
+    EventType === 'TransitionEvent' &&
+    window.TransitionEvent !== 'function'
+  ) {
+    const transitionEventProperties = [
+      'propertyName',
+      'elapsedTime',
+      'pseudoElement',
+    ]
+    transitionEventProperties.forEach(property => {
+      Object.defineProperty(event, property, {
+        value: eventInit[property],
+      })
+    })
+  }
+
   // DataTransfer is not supported in jsdom: https://github.com/jsdom/jsdom/issues/1568
   const dataTransferProperties = ['dataTransfer', 'clipboardData']
   dataTransferProperties.forEach(dataTransferKey => {