which uses e.target (which can be NULL if custom events are being used)

Firing a mousedown event without a target feels wrong, but maybe that's fine in the JavaScript land. Can we, from the logs, tell where the custom event is coming from?

In T406613#11250990, @Daimona wrote:

which uses e.target (which can be NULL if custom events are being used)

Firing a mousedown event without a target feels wrong, but maybe that's fine in the JavaScript land. Can we, from the logs, tell where the custom event is coming from?

event.target could be a text node so I think that's more likely the issue here since you are mixing a native event handler and jQuery code. I think you need to check event.target.nodeType === Node.TEXT_NODE

Change #1194302 had a related patch set uploaded (by Daimona Eaytoy; author: Daimona Eaytoy):

[mediawiki/core@master] diff.js: guard against events without target or text node target

https://gerrit.wikimedia.org/r/1194302

I'm still not 100% sure of what could cause this and would appreciate seeing it, but the fix above should do.

Change #1194302 merged by jenkins-bot:

[mediawiki/core@master] diff.js: guard against events without target or text node target

https://gerrit.wikimedia.org/r/1194302