keyCode 229 and Enter during IME composition

During IME composition, keydown often reports keyCode 229 (VK_PROCESSKEY on Windows) for many keys, meaning the event is part of an input method sequence. Enter may commit composition, insert a newline, or be swallowed—Chrome vs Firefox vs Japanese layouts differ. Handlers that assume Enter always means insertParagraph break composition incorrectly.

Problem Overview

Legacy keyCode / which APIs are deprecated but still used in hot paths. 229 is a sentinel: “handled by IME; don’t treat as a normal key.” Ignoring that and running custom Enter logic during isComposing causes double commits or cancelled composition.

Observed Behavior

• Enter fires with keyCode 229 during composition; beforeinput may carry insertLineBreak or composition commit depending on engine.
• Japanese IME: Enter to select first candidate vs newline differs by IME settings.

Impact

Duplicate lines, lost syllables, or editors that block Enter entirely during IME.

Browser Comparison

Chrome and Firefox dispatch different sequences around Enter + composition; macOS vs Windows keyboard stacks add variance.

Solutions

• Prefer e.isComposing and beforeinput inputType over raw keyCode for control flow.
• If you must use keydown, treat 229 as “possibly IME—do not insert structural nodes.”
• Test Japanese and Korean Enter behavior explicitly.

Related Cases

• ce-0210
• ce-0211
• ce-0212

References

• MDN: KeyboardEvent: keyCode (deprecated)
• UI Events