[Popup] We need a JS method to open the popup

[mfreed7]

Given the new approach for popup, and the associated resolution not to have a "live" open content attribute, there needs to be a way to open/reopen the popup via Javascript. The most straightforward would seem to be something like:

const myPopup = document.querySelector('div[popup]');
myPopup.show(); // or
myPopup.showPopup();

That would require adding a show() or showPopup() IDL method to HTMLElement. And then the question becomes: what happens if this is called on an element that lacks the popup attribute? Or for which the value of the popup attribute is invalid? I think it likely should do nothing, but it could also throw, and it could also add a valid popup attribute to the element. The last one feels odd, but I suppose it's an option.

[mfreed7]

I should have added, we also need a corresponding way to close the popup from Javascript:

myPopup.hide(); // or
myPopup.hidePopup();

That one likely should not throw and should not change any attributes. It should just be a no-op if the element isn't currently a top layer popup.

[mfreed7]

This has been added to the explainer, here.

const popup = document.querySelector('[popup]');
popup.showPopup(); // Show the popup
popup.hidePopup(); // Hide a visible popup