Fix custom change event listener

[muan]

Anyone can fire a custom change event. This ensures that it doesn't throw when event.detail is null. cc @latentflip

cc @github/web-systems

[latentflip]

Nice 👍 I think we also need to make a similar change here:

check-all/check-all.js

Lines 65 to 71 in 3432728

	function onCheckAllItem(event: Event): void {
	if (event instanceof CustomEvent) {
	const {relatedTarget} = event.detail
	if (relatedTarget.hasAttribute('data-check-all') || relatedTarget.hasAttribute('data-check-all-item')) {
	return
	}
	}

   function onCheckAllItem(event: Event): void {
-    if (event instanceof CustomEvent) {
+    if (event instanceof CustomEvent && event.detail) {
       const {relatedTarget} = event.detail
-      if (relatedTarget.hasAttribute('data-check-all') || relatedTarget.hasAttribute('data-check-all-item')) {
+      if (relatedTarget && relatedTarget.hasAttribute('data-check-all') || relatedTarget.hasAttribute('data-check-all-item')) {

         return
       }
     }

[latentflip]

@koddsson @muan what do you think about my comment here: #2 (comment)

[koddsson]

@koddsson @muan what do you think about my comment here: #2 (comment)

Looks good to me. I kind of wish that we didn't have to check all attributes to see if they are present but I think we probably need to if we are listening to the change event, huh?

[muan]

Release out 0.2.1