address regression for "Adaptive print version shows events with cust…

…om eventContent with zero height #7419"

contrib/react/src/index.tsx

@@ -63,6 +63,13 @@ export default class FullCalendar extends Component<CalendarOptions, CalendarSta
     })
     this.calendar.render()
 
+    // attaching with .on() will cause this to fire AFTER internal preact rendering did flushSync
+    this.calendar.on('_beforeprint', () => {
+      flushSync(() => {
+        // our `customRenderingMap` state will be flushed at this point
+      })
+    })
+
     let lastRequestTimestamp: number | undefined
 
     customRenderingStore.subscribe((customRenderingMap) => {

contrib/react/tests/index.jsx

@@ -721,6 +721,9 @@ it('render custom event JSX during print-mode', (done) => {
     const api = calendarRef.current.getApi()
     api.trigger('_beforeprint')
 
+    // HACK: this timeout is not accurate. printing should not rely on timeout.
+    // However, the feature ultimately works in live testing when triggering browser printing.
+    // TODO: refactor synchronicity
     setTimeout(() => {
       const eventEls = getEventEls(container)
       expect(eventEls[0].offsetHeight).toBeGreaterThan(10)