🚨 Error: Cannot read property '__AMP_TOP' of null

[ampprojectbot]

Details

Error report: link
First seen: May 4, 2020
Frequency: ~ 1,167/day

Stacktrace

Error: Cannot read property '__AMP_TOP' of null
    at win (src/service.js:325:9)
    at getTopWindow (src/service.js:199:8)
    at getService (src/service.js:378:62)
    at getAmpdoc (src/service.js:251:17)
    at getServiceForDoc (extensions/amp-analytics/0.1/variables.js:449:9)
    at variableServiceForDoc (extensions/amp-analytics/0.1/config.js:62:28)
    at extensions/amp-analytics/0.1/amp-analytics.js:231:32
    at loadConfigTask (extensions/amp-analytics/0.1/amp-analytics.js:237:10)

Notes

@cramforce modified src/service.js:325-325 in #23767 (Aug 7, 2019)
@choumx modified src/service.js:193-202 in #10131 (Jun 28, 2017)
@rsimha modified src/service.js:378-381 in #21212 (May 16, 2019)
@choumx modified src/service.js:246-255 in #16328 (Jun 29, 2018)
@calebcordry modified extensions/amp-analytics/0.1/variables.js:448-449 in #22300 (May 17, 2019)
@zhouyx modified extensions/amp-analytics/0.1/config.js:60-62 in #28174 (May 4, 2020)
@zhouyx modified extensions/amp-analytics/0.1/amp-analytics.js:235-239 in #27605 (Apr 20, 2020)

Seen in:

• 05-05 Beta (0322)
• 05-05 Experiment-A (0322)
• 05-05 Experimental (0322)
• 05-06 Nightly (2312)
• +2 more

Possible assignees: @cramforce, @calebcordry

/cc @ampproject/release-on-duty

[rcebulko]

Seems to be a variant of #9177 , but this one appeared as soon as the May 5 release hit Nightly and later spiked when that release was promoted to beta/experimental.

@zhouyx It seems likely this is related to #28174 , possibly a race condition.

[rcebulko]

[zhouyx]

👀

[zhouyx]

I found two related changes.

1. Expand analytics variables in remote config url #28174 as @rcebulko mentioned. The PR added variableServiceForDoc(element).
   Or
2. Turn on analytics-chunks in canary #28069. This PR turned on analytics-chunks in canary. it delays the call of the loadConfig, and thus increase the frequency of the error.

[zhouyx]

After some investigation. I think it's most likely due to #28069.

Reason being we have:

amphtml/extensions/amp-analytics/0.1/config.js

Line 220 in c985e34

Services.urlReplacementsForDoc(this.element_)

If there's a race condition, the Services.urlReplacementsForDoc(this.element_) should throw the same error before.
I can add additional check to this.win_ != null if that's helpful.

Add @choumx @jridgewell for fixing ideas.

[dreamofabear]

Nice catch and thanks for the quick debugging and response. What's the race condition?

[zhouyx]

Read from

amphtml/src/types.js

Lines 85 to 89 in c985e34

	/**
	* Externs declare that access `defaultView` from `document` or
	* `ownerDocument` is of type `(Window|null)` but most of our parameter types
	* assume that it is never null. This is OK in practice as we ever only get
	* null on disconnected documents or old IE.

My understanding is that element.ownerDocument.defaultView is null and the race condition is that the document is disconnected.

My guess on the error above:

amphtml/extensions/amp-analytics/0.1/amp-analytics.js

Lines 234 to 236 in c985e34

	if (isExperimentOn(this.win, 'analytics-chunks') && !this.isInabox_) {
	chunk(this.element, loadConfigTask, ChunkPriority.HIGH);
	} else {

With the analytics-chunk experiment, the document somehow is disconnected before we call loadConfig?

[dreamofabear]

Ah ok, it's the same issue. The root fix is probably removing toWin() and unsafe casting.

[stale]

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.