Intent to Implement and Ship: beforeprint and afterprint events

[TAMURA, Kent]

Contact emails

tk...@chromium.org

Spec

https://html.spec.whatwg.org/multipage/timers-and-user-prompts.html#printing-steps

Summary

Synchronous events dispatched before and after printing.

Motivation

- This feature is helpful to make and clean printing-only content which can't be implemented with CSS media query.

- Edge, Firefox, and IE have shipped it for years.

Interoperability and Compatibility Risk

Very low. Small additional feature.

Edge: Shipped

Firefox: Shipped

Safari: No signals

Web developers: Positive. The feature request bug has 42 stars.

Ongoing technical constraints

None.

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)?

Yes.

OWP launch tracking bug

crbug.com/218205

Link to entry on the feature dashboard

https://www.chromestatus.com/features/5700595042222080

Requesting approval to ship?

Yes.

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TAMURA Kent
Software Engineer, Google

[TAMURA, Kent]

Oops, missed wpt section.

Is this feature fully tested by web-platform-tests?

Multiple test files in WPT check existence of onbeforeprint and onafterprint attributes, however I think there are no tests for event dispatching. It's difficult to test printing with interoperable ways.

[PhistucK]

I think printing is sort of asynchronous in Chrome (which causes or has caused web development issues) - interoperability here is very important, so I am not really sure how, but I think this needs to be tested for interoperability extensively, otherwise this feature may be rendered useless in Chrome.

☆PhistucK

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[Philip Jägenstedt]

AFAIK, you're right that this couldn't currently be tested without adding some bits of infrastructure, so I've filed https://crbug.com/738393 to track that.

If you'd like, you can still write a manual test for this, I did something related in https://github.com/w3c/web-platform-tests/pull/970 a few years ago. Manual tests aren't super valuable right now, so it's up to you.

LGTM1, thanks for taking care of these cases where we are the last to ship, I'm confident that web developers will appreciate it!

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[Mike West]

LGTM2.

-mike

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[Chris Harrelson]

LGTM3

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[TAMURA, Kent]

If we still have asynchronous issues like crbug.com/449109, adding afterprint event might introduce another pattern of unable-to-print issues.  We should check the current behavior, and should fix existing issues before implementing afterprint.

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