Fix ESLint errors

I'm interested to see what you change to fix this. I also have error Prefer matches to $.is jquery/no-is for source lines that were using .is(':checked')

Created this MR which should fix this.

However, not trivial to find out what Prefer matches to $.is is supposed to mean, for a JS non-expert.

Yes JS is one of the mysteries I understand the least about :-)
If found https://github.com/wikimedia/eslint-plugin-no-jquery/blob/master/docs/ru... which I think is explaining the rule.

I presume you have javascript test coverage for the behaviours function you are changing? Would it be worth making an incorrect change, eg swapping over the 'enabled' and 'disabled' text, to prove it?

No, I don’t think these are covered by our FunctionalJavascript tests. I just tried it out manually and it works fine.
Thanks for finding the docs! However, the “correct code” examples they give do not work for me, and also aren’t consistent with the error message that says matches() should be used instead. So, they don’t seem very helpful.

Anyways, I think we can just merge this, should be fine.