Uncaught TypeError: Cannot read property 'offsetWidth' of null about unpoly HOT 2 CLOSED

I'm not familiar with UIKit, so I can only guess:

It looks like UIKit is using MutationObserver to run JavaScript whenever an element enters or leaves the DOM. Unpoly replacements manipulate the DOM, so UIKit JavaScript will run when Unpoly changes anything.

The stack trace above shows that you're using the up-keep attribute. To process up-keep elements, Unpoly needs to temporarily detach keepable elements from the DOM. It looks like UIKit runs its JavaScript on detached elements, but crashes because it cannot find the element's scrolling viewport (to measure scroll positions or something).

The major change in Unpoly 0.50+ is that we're now using native promises instead of jQuery deferreds. This means that async code now runs in the next microtask instead of the next task. This may have changed the order in which async code in Unpoly and UIKit is scheduled.

You could try to make your app work without [up-keep], but it doesn't change the underlying issue that UIKit seems to assume that it is the only code working with the DOM.

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Thank you, this information will be helpful.

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