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Uncaught TypeError: observer.unobserve is not a function
Closed, ResolvedPublicBUG REPORT

Description

What is the problem?

When opening the Visual Editor, I am sometimes seeing the error in the browser console:

Uncaught TypeError: observer.unobserve is not a function
    at <anonymous>:242:484
    at Object.fire (<anonymous>:622:949)
    at VeInitMwDesktopArticleTarget.ve.init.mw.DesktopArticleTarget.transformPage (<anonymous>:22:323)
    at VeInitMwDesktopArticleTarget.ve.init.mw.DesktopArticleTarget.activate (<anonymous>:8:684)
    at <anonymous>:142:236
    at mightThrow (load.php?lang=en&modules=ext.CodeMirror.lib|ext.centralNotice.bannerHistoryLogger%2CchoiceData%2Cdisplay%2CimpressionEventsSampleRate%2CkvStore%2CstartUp|jquery%2Coojs-ui-core%2Coojs-ui-widgets|jquery.ui|mediawiki.diff|wikibase.client.linkitem.init&skin=vector&version=wkhrv:351)
    at process (load.php?lang=en&modules=ext.CodeMirror.lib|ext.centralNotice.bannerHistoryLogger%2CchoiceData%2Cdisplay%2CimpressionEventsSampleRate%2CkvStore%2CstartUp|jquery%2Coojs-ui-core%2Coojs-ui-widgets|jquery.ui|mediawiki.diff|wikibase.client.linkitem.init&skin=vector&version=wkhrv:352)

The error appears to happen here.

It does not always happen. I am not sure the exact steps to reproduce reliably.

Steps to reproduce problem
  1. Find an article
  2. Open the browser console
  3. Open Visual Editor
Environment

Browser: Chromium 87, Firefox 78
Wiki(s): https://en.wikipedia.beta.wmflabs.org

  • MediaWiki 1.38.0-alpha (5ab8904) 14:16, 6 December 2021.
  • Vector 1.0.0 (2088dd9) 07:22, 6 December 2021.
  • VisualEditor 0.1.2 (0978f3f) 10:49, 6 December 2021.

Event Timeline

Change 747631 had a related patch set uploaded (by Bartosz Dziewoński; author: Jdlrobson):

[mediawiki/skins/Vector@master] Don't use ts-ignore. It is hiding real errors

https://gerrit.wikimedia.org/r/747631

Change 747631 merged by jenkins-bot:

[mediawiki/skins/Vector@master] Don't use ts-ignore. It is hiding real errors

https://gerrit.wikimedia.org/r/747631

matmarex assigned this task to Jdlrobson.
matmarex added a subscriber: matmarex.

Change 751543 had a related patch set uploaded (by Clare Ming; author: Jdlrobson):

[mediawiki/skins/Vector@wmf/1.38.0-wmf.13] Don't use ts-ignore. It is hiding real errors

https://gerrit.wikimedia.org/r/751543

Change 751543 merged by jenkins-bot:

[mediawiki/skins/Vector@wmf/1.38.0-wmf.13] Don't use ts-ignore. It is hiding real errors

https://gerrit.wikimedia.org/r/751543

Mentioned in SAL (#wikimedia-operations) [2022-01-05T19:27:28Z] <urbanecm@deploy1002> Synchronized php-1.38.0-wmf.13/skins/Vector/resources/skins.vector.es6/stickyHeader.js: f6424f32611bce8d9e95c369c28e2f787e2cdf75: Dont use ts-ignore. It is hiding real errors (T297119) (duration: 01m 08s)