`popovertarget` and shadow DOM

[jpzwarte]

So in this example from https://html.spec.whatwg.org/multipage/popover.html#the-popover-target-attributes

<button popovertarget="foo" popovertargetaction="show">
  Show a popover
</button>

<article popover=auto id="foo">
  This is a popover article!
  <button popovertarget="foo" popovertargetaction="close">Close</button>
</article>

The close button will not work if <article> is a custom element instead. This is a pretty common thing with shadow DOM: ids are scoped to the shadow root.

It would be awesome though if the example above could work with custom elements.

Perhaps add popovertarget=":host" to the spec?

[jpzwarte]

Trying to make sure this isn't lost in the noise: cc @jakearchibald

[jakearchibald]

cc @mfreed7

The proposal seems reasonable to me, but we should think about it carefully as it'll likely become "the way to do it" for similar features in future.

@annevk @domenic has this come up with custom elements before?

[keithamus]

There already exists an imperative API for cross root bindings. To extend your example with functioning code:

<button popovertarget="foo" popovertargetaction="show">
  Show a popover
</button>

<my-article popover=auto id="foo">
  <template shadowrootmode="open">
    This is a popover article!
    <button popovertargetaction="close">Close</button>
  </template>
</my-article>

class MyArticle extends HTMLElement {
  static {
    customElements.define('my-article', this)
  }
  connectedCallback() {
    this.shadowRoot.querySelector('button').popoverTargetElement = this
  }
}

[keithamus]

Refs https://github.com/openui/open-ui/issues/651

[jpzwarte]

@keithamus Thanks; I was kind of hoping I wouldn't need to write JS for this, but fair enough.

[Westbrook]

There does need to be an declarative API, at some point. Would be best to push on this early, and set a standard for other specs whereby this detail isn't left out of proposals in the future. There are some similar concepts going around within the AOM for cross root aria, maybe room to align techniques?

[keithamus]

Needs label https://github.com/whatwg/html/labels/topic%3A%20popover

[gfellerph]

There is also the opposite case where the popover is in the shadow DOM and the button in the light DOM should invoke it:

https://codepen.io/tuelsch/pen/LYMvmva

<test-popup>hello, this is a test</test-popup>
<button popovertarget="testpopup">this should cross shadow boundaries and trigger a popup</button>

const template = document.createElement("template");

template.innerHTML = `
  <div popover id="testpopup">
    <slot></slot>
  </div>
`;

class TestPopup extends HTMLElement {
  constructor() {
    super();
    this._shadowRoot = this.attachShadow({ mode: "open" });
    this._shadowRoot.appendChild(template.content.cloneNode(true));
  }
}

customElements.define("test-popup", TestPopup);

Not sure if this use-case should be handled as well.

[lukewarlow]

I've recently come across the limitations with this cross-root popover API, it would be very nice if you could use the IDL to assign elements truly cross root. e.g. button in light dom, popover in shadow or button in shadow, popover in shadow.

If you have the element reference you already have full access to the shadow tree so I don't think this would expose anything you don't already have?

[Westbrook]

Assigning ID references across root without having full access to the child root is proposed to work along these lines. Things like popovertarget are included specifically.

However, something fully declarative here would be quite nice and should likely be a requirement, at some point.