transitioning class is sometimes not removed

[Megamouse]

Chrome and Firefox:
Sometimes, when putting nested children with conditional maps inside of the open Slidedown, the endTransition function won't be called after some child component was mounted.

My guess is that the onTransitionEnd event won't always be fired for some reason, but I haven't found out why yet.

[DiFuks]

This problem occurs in this line:

https://github.com/frankwallis/react-slidedown/blob/master/lib/slidedown.tsx#L92

Suppose that when changing the component props, its height has not changed, and closed = true. Then

    endHeight = getComputedStyle(this.outerRef).height

The endHeight variable will turn out to be "auto".
The line below parseFloat (endHeight) will return "NaN", the condition will be satisfied, and the transitioning class will be assigned to the component.

if (parseFloat(endHeight).toFixed(2) !== parseFloat(prevHeight).toFixed(2)) {
    this.outerRef.classList.add('transitioning')
    // ...
}

The animation is not triggered, and the endTransition method will not be called, since the height has not changed. Therefore, the transitioning class will remain with the component.

As a solution, I see:
To get the height of a component is not using getComputedStyle, but getBoundingClientRect. So it is used in getSnapshotBeforeUpdate.

[jameswilson]

I can confirm this bug affects nested <SlideDown> components where the outer component defaults to open, and the inner component defaults to closed.

Here is a sandbox demonstrating the bug:
https://codesandbox.io/s/eloquent-zhukovsky-p2lo7?file=/src/App.js