Bug: In react 18, flashing effect appears at the end of exit phase before entering

[tranvansang]

What is the current behavior?

When clicking the button

• Phase 1: current element's opacity = 1
• Phase 2: current element's opacity becomes 0 (with animation/transition)
• Phase 3 (bug, react 18 ONLY): current element's opacity becomes 1 without animation/transition
• Phase 4: current element disappears
• Phase 5: next element opacity appears with opacity = 0
• Phase 6: next element's opacity becomes 1 (with animation/transition)

What is the expected behavior?

Phase 3 shouldn't exist in react 18 renderer.

Could you provide a CodeSandbox demo reproducing the bug?

In demo's index.js, try changing legacyReact value to switch react 18 behav

2022-04-12.08-15-18.mp4

ior.

https://codesandbox.io/s/wonderful-glade-n0n92s?file=%2Fsrc%2Findex.js

[sotarules]

Friends, I have what I believe is the same issue, but in my case I'm animating a slide transition from right-to-left using 3D translate affecting the X value.

The "new" component enters from the right, while the "old" component simultaneously exits to the left.

What I'm seeing a perfectly executed transition until the very end, and then you see a brief flash of the old exiting component superimposed over the newly-entered component.

In theory, it should be impossible to see the old exited component at the end of the animation because the 3D translate rules, if processed as designed, would mean the exited component X value would place the old component 100% off screen. There should be no way to "see" the brief flash of the old exited component.

I am confident that the cause of this problem is the React 18 update batching, because I've been able to ameliorate the problem by doing the safeSetState using flushSync.

IMPORTANT: It is apparently only necessary to "wrap" the nextState value of exited with flushSync; all other nextState values (entering, entered, exiting) can be done using setState in the normal manner.

I believe that state-transitions exiting and exited are being erroneously combined into a single batch update by React 18.

This cannot be permitted, or the animation will be impacted.

The updates for exiting and exited must not be batched.

It is necessary to fully process the exiting state before setting exited state.

I hope this makes sense, this stuff is very complicated and hard to get your head around. Here is my fix.

 safeSetState(nextState, callback) {
      // This shouldn't be necessary, but there are weird race conditions with
      // setState callbacks and unmounting in testing, so always make sure that
      // we can cancel any pending setState callbacks after we unmount.
      callback = this.setNextCallback(callback)
      this.setStateConditionalFlushSync(nextState, callback)
  }

  /**
   * Prevent React 18 from batching updates.
   *
   * @param {object} nextState Next state object.
   * @param {function} callback Post-set callback.
   */
  setStateConditionalFlushSync(nextState, callback) {
      console.log(`Transition.js setStateConditionalFlushSync nextState=${JSON.stringify(nextState)}`)
      if (nextState?.status !== "exited") {
          console.log(`Transition.js setStateConditionalFlushSync *imperative* nextState=${JSON.stringify(nextState)}`)
          this.setState(nextState, callback)
          return
      }
      flushSync(() => {
          console.log(`Transition.js setStateConditionalFlushSync *flushSync* nextState=${JSON.stringify(nextState)}`)
          this.setState(nextState, callback)
      })
  }

[tranvansang]

@sotarules

thanks!! so much, buddy.

I have patched the package using your fix, and now it WORKs LIKE A CHARM!!

[jcampuza]

It doesn't seem to me this was ever fixed/released even though this is marked as completed?

[tranvansang]

not fixed yet with the recently released version 4.4.5

here is the commit to fix c20af7c

[asapach]

not fixed yet with the recently released version 4.4.5

are there any plans to fix this and release a new version?

[ermolaev-frontend]

This bug is still relevant.

[ermolaev-frontend]

This bug is still relevant.

[sergei-startsev]

@tranvansang is there a chance to release a new version with the fix?