caniuse | Raw browser/feature support data from caniuse.com | Dataset library

Vue3 relies on Proxy for handling reactivity. Even if you can get around some functionalities, adjusting the core code to use Proxies is a non-trivial endeavor, and is, AFAIK, the main reason that Vue3 does and will not support IE11.

You will either need to continue using Vue2, or alternatives like Svelte that can generate ES5 bundles.

Therefore you have extra JS files in your file structure.

And in your attempts, they are mixed with your Meteor project structure, in a build folder (when you use command meteor build build --directory) or directly merged (meteor build .. --directory).

Therefore, on the next build run, Meteor picks these extra JS files as if they were part of your source code (eager loading), and fails, as suggested in the warning message:

The output directory is under your source tree. Your generated files may get interpreted as source code! Consider building into a different directory instead meteor build ../output

It would have worked in your next attempt if you had specified an explicit sibling build folder, instead of just the parent folder (which therefore puts files directly in your Meteor project root), e.g. meteor build ../siblingFolder

Another possible workaround is to use a build folder name starting with a dot ., so that Meteor ignores it on the next runs when it looks for source code, e.g. meteor build ./.build

See special directories docs:

The following directories are also not loaded as part of your app code:

• Files/directories whose names start with a dot, like .meteor and .git

In my question I wrote:

If I were using marked-up images, declaring one or more fallback images is elementary [...]

But (sigh) in this instance, the images are CSS background-images, so options for creating fallbacks are more limited

And for now, at least, - ie. while we're still waiting (in 2022) for widespread cross-browser support for the CSS image-set() function - that's true.

While I was hunting around for alternative approaches, I unexpectedly came across this July 2021 comment by Quentin Albert:

For what most people use background images for you can nowadays easily use object-fit + object-position.

Source: https://css-tricks.com/using-performant-next-gen-images-in-css-with-image-set/

This was news to me. I was dimly aware of the object-fit CSS property, but I'd never come across the object-position CSS property at all.

But it absolutely works!!

If image-set() had extensive cross-browser support, this was my intended CSS, which would enable a fallback image for Safari:

Remove display: flex and it works:

You can read about viewing the iOS console. You need to connect your iOS device to a mac, then use the Safari on that mac, to do that. It's a pain in the xxx neck. Explaining how is beyond the scope of a Stack Overflow answer.

Or you can use alert() for debugging.

You need to call cameraView.play() at the right moment. Here's the documentation.

It recommends doing something like this.

You can do that like so: