Can't prevent `touchmove` from scrolling window on iOS

Question

We are trying to scroll an element on our iOS web app while preventing the window itself from scrolling. We are capturing the touchmove event on the window, scrolling the element programmatically and (trying to) prevent the window itself from scroll by calling preventDefault on the event.

Unfortunately this doesn't work in Mobile Safari. The window continues to scroll underneath our element. The issue sounds exactly like the Webkit bug described in https://bugs.webkit.org/show_bug.cgi?id=163207, but that issue was supposedly fixed in iOS 10.3 whereas I am running 11.3.

Catching touchforcestart and calling preventDefault does seem to prevent scrolling of the window, but we are calling it in touchstart, which seems to be "too late" since the window still scrolls. Scrolling is only prevented next time touchstart is called.

Any ideas about what is going on? We are baffled since this is clearly a bug but it seems to have been fixed some time ago.

Answer 1

I recently ran into this same problem. You'll need to pass { passive: false } when registering the touchmove event listener. e.g.

document.addEventListener('touchmove', function(e) {
    e.preventDefault();
}, { passive: false });

This is because document touch event listeners are now passive by default in Safari 11.1, which is bundled with iOS 11.3. This change is documented in the Safari 11.1 release notes:

Web APIs

• [...]
• Updated root document touch event listeners to use passive mode improving scrolling performance and reducing crashes.