Amphtml: position-observer: Safari scroll-bound animation only working one direction

[afilbert]

What's the issue?

Scroll-bound animations using direction: "alternate" stop working on Safari when amp-position-observer scrolls up out of view.

How do we reproduce the issue?

1. Go to example pen: https://codepen.io/aghassemi/full/dzKGWy/
2. Scroll all the way down to the bottom of the pen. Notice the animation is working.
3. Scroll back up, and the animation won't reengage.

_This seems to be the case using direction: "alternate"._ Setting to direction: "reverse-alternate" appears to work as expected.

What browsers are affected?

Tested versions:

• Desktop Safari Version 10.1.1 (12603.2.4)
• Mobile Safari Version 10.0 on iOS 10.3.3

Which AMP version is affected?

v0, v0.1 for amp-position-observer

[afilbert]

Awesome, I got a palindrome issue number. :)

[aghassemi]

on it

[aghassemi]

Interesting that direction: "reverse-alternate" works! Value of direction should not really make a difference, will look into it.

[afilbert]

Thanks for taking a look, and for your quick response @aghassemi!

[rudygalfi]

Setting back to Backlog Bugs. We need to determine new milestone @aghassemi @ericlindley-g

[ampprojectbot]

This issue hasn't been updated in awhile. @aghassemi Do you have any updates?

[ampprojectbot]

This issue hasn't been updated in awhile. @aghassemi Do you have any updates?

[nainar]

Interestingly, this also repros in Edge. Edge, Safari both don't support Web Animations API (the demo here doesn't work in Edge & Safari). Which means we fallback to our polyfill in this case. I would hazard a guess that the polyfill is goofing up here and that it only manifests in Safari, Edge because they use it. Tracking this down.

@aghassemi mind if I assign this to myself?

[aghassemi]

Go for it

[ampprojectbot]

This issue hasn't been updated in awhile. @nainar Do you have any updates?

[ampprojectbot]

This issue hasn't been updated in awhile. @nainar Do you have any updates?

[nainar]

Removing myself - this was not a trivial fix from what I remember. Hazy on the details.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 7 days if no further activity occurs. Thank you for your contributions.