🚨 Error: Cannot read property 'sourceElement' of undefined

[ampprojectbot]

Details

Error report: link
First seen: Jul 23, 2019
Frequency: ~ 2,108/day

Stacktrace

Error: Cannot read property 'sourceElement' of undefined
    at extensions/amp-lightbox-gallery/0.1/amp-lightbox-gallery.js:646:14
    at src/core/data-structures/observable.js:78:6
    at fire (src/gesture.js:437:17)
    at signalEmit (src/gesture-recognizers.js:400:9)
    at emit_ (src/gesture-recognizers.js:355:9)
    at acceptStart (src/gesture.js:536:15)
    at doPass_ (src/gesture.js:469:11)
    at afterEvent_ (src/gesture.js:299:9)

Notes

Sepand Parhami modified extensions/amp-lightbox-gallery/0.1/amp-lightbox-gallery.js:644-646 in #22232 (May 16, 2019)
@erwinmombay modified src/core/data-structures/observable.js:78-78 in #4249 (Sep 9, 2016)
@rsimha modified src/gesture.js:437-439 in #21212 (May 16, 2019)
@rsimha modified src/gesture-recognizers.js:400-415 in #21212 (May 16, 2019)

Seen in:

• 05-15 Beta (0310)
• 05-15 Experiment-B (0310)
• 05-15 Experimental (0310)
• 05-21 Nightly (0438)
• +2 more

/cc @ampproject/release-on-duty

[Enriqe]

/cc @caroqliu @micajuine-ho

[caroqliu]

Swiped around on my iPhone and nothing is standing out... @micajuine-ho any ideas?

One note - I'm surprised that we are getting undefined here when the helper uses devAssert, shouldn't we be able to expect to see logs for those assertion failures as well? cc @rcebulko

amphtml/extensions/amp-lightbox-gallery/0.1/amp-lightbox-gallery.js

Line 646 in 2dd14e5

const {sourceElement} = this.getCurrentElement_();

amphtml/extensions/amp-lightbox-gallery/0.1/amp-lightbox-gallery.js

Lines 677 to 682 in 2dd14e5

	getCurrentElement_() {
	const lbgId = this.currentLightboxGroupId_;
	const currentElement = devAssert(
	this.elementsMetadata_[lbgId][this.currentElemId_]
	);
	return currentElement;

[rcebulko]

Duplicate of #26914 that was seen as a new error because observable.js was moved, so the stacktrace appears distinct.

@caroqliu all devAssert calls are removed from builds during compilation, so nothing would be logged.