Fix issue #523 - "Slider cannot be initialized in iframe"

[jayelkaake]

How to recreate the issue

Load glide in an iframe

What I Did

I changed the exist() method to use duck-typing instead of a null check.

The work that @ericmorand did in pull request #669 did not fully solve the problem, and also sort of makes it possible to pass invalid objects, so was not a preferred solution. Thanks for leading me in the right direction though @ericmorand!

How was it tested

Loaded in iframe and out of iframe.

[stokesman]

I agree that this seems like a better fix. However, I think it would be possible to avoid duck-typing by using ownerDocument.defaultView. Mostly I'm adding the comment because it seems like ownerDocument and defaultView are oft overlooked features of the DOM.

Suggested change

	// We are usine duck-typing here because we can't use `instanceof` since if we're in an iframe the class instance will be different.
	if (node && node.appendChild && node.isConnected) {
	if (!node) return false
	const nodeWindow = node.ownerDocument?.defaultView
	if (nodeWindow && node instanceof nodeWindow.HTMLElement) {

I’d also probably just return the test nodeWindow && node instanceof nodeWindow.HTMLElement directly and eliminate the following returns but couldn’t do that in the scope of the suggestion.