Feature/811 once and context

[markconroy]

Closes #811

[ctorgalson]

Late review, sorry.

TL;DR: I think this is good but needs a guard clause to complete #811; I didn't have a chance to test it.

Using .once() will only return DOM elements once, but I think the behavior will still run multiple times.

The second part we usually add is one or more guard clauses (see suggestion). This makes sure that, on subsequent runs, the behavior doesn't try to do anything and exits immediately.

For example, if this behavior ran twice, the first go would mark the menu and toggle with a data-once attribute and continue through the code. But on the second iteration, I think the two variables will be undefined, and line 17 will try to add an event listener to an undefined element.

[ctorgalson]

Suggested change

	const [subsitesMenu] = once('allSubsitesMenuToggles', '.subsite-extra-menu', context);
	const [subsitesMenu] = once('allSubsitesMenuToggles', '.subsite-extra-menu', context);
	if (!subsitesMenuToggle || !subsitesMenu) {
	return;
	}

This is untested, but it's the usual defensive companion to .once().

[markconroy]

Thanks @ctorgalson, I've added in the extra defensive clause now. Let me know if you think we're missing any thinbg.

[finnlewis]

For reference: https://www.drupal.org/docs/drupal-apis/javascript-api/javascript-api-overview#s-example-using-drupalbehaviors