window.open should support the 'fullscreen' option

[cterefinko]

Without the 'fullscreen' option, the window must first be opened on the target display, and then requestFullscreen must be used. This option is currently marked as future work.

[michaelwasserman]

One alternative here is making some affordance for Element.requestFullscreen() on newly opened windows when the Window Placement permission is granted. That would be similar to existing affordances on screen orientation changes, and proposed affordances on screen configuration changes. See similar thoughts here: w3c/presentation-api#476 (comment)

[michaelwasserman]

This same idea got bumped by feedback from another potential partner.

[michaelwasserman]

Perhaps window.open(url, name, "fullscreen=true") could automatically make document.documentElement fullscreen.

• Should this only be the case for popup windows opened by window.open, not new tabs, etc.?
• The target screen would have to be inferred from the provided/default feature string bounds
  This is a reasonable enhancement to consider in the future.

[michaelwasserman]

Gathering explicit use case statements from web application developers would be valuable. For example, I can imagine multi-monitor virtual desktop software might want to open a fullscreen window on each display when the user connects to a remote or virtualized machine session. #7, #92, and #98 are all somewhat interrelated.

[NielsLeenheer]

Support for this would be fantastic!

We are currently experimenting with using the window placement API on Point of Sale machines with two integrated displays. The main display would run a web app for the cash register. The other display is facing the customer and would need to show the receipt.

Having the ability to open a window full screen on the second monitor would be really helpful.

[bradtriebwasser]

I'm created an explainer for this feature on a separate repository:

https://github.com/bradtriebwasser/fullscreen-popup/blob/main/EXPLAINER.md

Any feedback on the explainer is encouraged!

[tungnh28]

I am thinking in addition to gating behind "window placement", we might have to handle the case "fullscreen" is not alllowed by permission policy. For example window.open(url) comes with a header Permission-Policy: fullscreen=().
Should we give a notice and escape fullscreen mode in the cases?
@bradtriebwasser WDYT?