PSA: Fire beforeinput event before compositionupdate event during IME composition.

[Siye Liu]

Hi blink-dev,

We've been landing a change to enable new event ordering for beforeinput and compositionupdate during IME composition.

The previous event ordering for IME composition was:

keydown -> compositionstart -> beforeinput -> compositionupdate -> input -> keyup -> keydown -> beforeinput -> compositionupdate -> textInput -> input -> compositionend -> keyup.

The new ordering is:

keydown -> compositionstart -> compositionupdate -> beforeinput -> input -> keyup -> keydown -> compositionupdate -> beforeinput -> textInput -> input -> compositionend -> keyup.

This change aligns our event ordering with the behavior of Firefox and Safari, which fire the beforeinput event after the compositionupdate event.

The new event ordering is controlled by a runtime enabled feature flag that is set to stable status (enabled by default).

[Mike Taylor]

Hi there -

Given that this change is web observable, have you all done any compatibility testing or analysis to ensure sites aren't relying on the differences between engines here (hopefully not, but you know...)?

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[Gary Kačmarčík (Кошмарчик)]

FWIW, according to https://bugs.chromium.org/p/chromium/issues/detail?id=1484762 we previously had compositonupdate->beforeinput but inadvertently changed it to the current order around M52.

To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/b56a3104-8f16-4d60-95ab-62b8705c4a7f%40chromium.org.

[Siye Liu]

Hi Mike,

I haven't done compatibility testing because Chromium's behavior was introduced in M53 by accident. We previously had the correct input event sequence. The commit 65dc0072cfd947170ef4dbee2dd1f4c7c399156f - chromium/src - Git at Google (googlesource.com) is to fix the bug.