Asynchronous print events to load deferred images #2532
Description
At Wikimedia, we've discovered many of our users are working round slow internet connections by saving web pages and sharing them with each other via Whatsapp and other tools. Users typically print by using the browser print method. As a result, we've been trying to improve the printed experience for all our mobile web pages.
We've hit a problem with showing images in the printed versions of our pages as we lazy load images on Wikipedia to save our users data [1].
When printing an article, any lazy loaded images are not present in the printed version of the page.
This is not a unique problem to us, many other websites lazy load images e.g. try hitting print on any medium.com article with images.
Ideally we'd like to be able to subscribe to something akin to an onbeforeprint or event on MediaQueryList event and load images.
Obviously, making this event asynchronous leaves open potential abuse - it could mean the print function freezes altogether (unless a timeout is present) or is slow (imagine an event that downloads a 1gb file before allowing a print), but it should provide some support in loading of additional resources.
Any thoughts?
[1] https://blog.wikimedia.org/2016/09/19/mobile-web-improvements/