importNode should allow null customElementRegistry

[sorvell]

What problem are you trying to solve?

Currently importNode's ImportNodeOptions customElementRegistry cannot be null.

Because elements with null registries receive the document registry upon adoption, this means that it's not possible to call document.importNode, for example, on a template's content fragment and retain a null custom element registry.

While this is an unusual use case, it can come up when creating elements while the intended registry is not yet available.

What solutions exist today?

It's possible to workaround this by creating elements imperatively, but this is cumbersome.

How would you solve it?

Allow null to be set for importNode's customElementRegistry option and honor it as the fallback registry.

Anything else?

Migrated, see whatwg/html#12396 (comment)

[rniwa]

While this is an unusual use case, it can come up when creating elements

Do you mean that you've found such a use case? Or are you speculating that there might be such a use case?

[sorvell]

A use case

1. I have a template I'd like to render dynamically based on a route parameter.
2. it contains has custom elements, and I'd like to make sure they upgrade in document order to simplify potential initial event dispatch (a parent always see an event a child fires).
3. To be efficient, I want to render the DOM while the elements are loading and defining.

// load elements
container.append(document.importNode(template.content, {customElementRegistry: null});
// elements loaded...
customElements.initialize(container);

[rniwa]

But is that use case something you encountered while working on something, or is it a theoretical use case you thought of?

[sorvell]

But is that use case something you encountered while working on something, or is it a theoretical use case you thought of?

I had this need while developing an app. It's a work in progress about which I can't share specific details. Scoped registries are a new feature so this wasn't load bearing, but I realized it would be really helpful if I could import and use DOM from a template, since it's an easy and efficient, but not worry about work being done to prepare a registry until ready to use it.