Scenario

Duplicate beforeinput or input events during IME composition

Some browsers and keyboards emit duplicate composition-related input or beforeinput events—especially iOS Safari dictation paths and certain Android keyboards—so naive handlers that insert text on every input may double characters or corrupt state.

ime

Scenario ID

scenario-ime-composition-duplicate-events

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Details

Some browsers and keyboards emit duplicate composition-related input or beforeinput events—especially iOS Safari dictation paths and certain Android keyboards—so naive handlers that insert text on every input may double characters or corrupt state.

Problem Overview

Frameworks often assume one input per user intent. IME and voice pipelines can replay or split events.

Observed Behavior

iOS Safari: extra input after dictation or composition end.
Android: first-word duplication with prediction enabled.

Impact

Duplicate text, broken undo, model–DOM drift in React-controlled editors.

Solutions

Deduplicate using a hash of (inputType, data, selection position) in a short window, or ignore input while a transaction is in flight.
Prefer beforeinput cancellation paths when you fully control insertion.

References

scenario-ios-safari-contenteditable-do-not-force-rerender-or-change-selection-during-input — related iOS sync issues

Scenario flow

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Variants

Each row is a concrete case for this scenario, with a dedicated document and playground.

Case	OS	Device	Browser	Keyboard	Status
ce-0096-ime-composition-duplicate-events-ios-safari	iOS 17.0	iPhone or iPad Any	Safari 17.0	Korean (IME)	draft
ce-0577-android-first-word-duplication	Android 14.0	Smartphone Any	Chrome 131.0	Gboard (English/Korean)	confirmed

Browser compatibility

This matrix shows which browser and OS combinations have documented cases for this scenario. Click on a cell to view the specific case.

Browser	Android	iOS
Chrome	ce-0577-android-first-word-duplication 131.0	—
Safari	—	ce-0096-ime-composition-duplicate-events-ios-safari 17.0

Confirmed

Draft

— No case documented

Cases

This scenario affects multiple languages. Cases are grouped by language/input method below.

Gboard (English/Korean)

1 case

Android: First word duplication after space + backspace

OS: Android 14.0 · Device: Smartphone Any · Browser: Chrome 131.0

Open case →

Korean

1 case

IME composition triggers deleteContentBackward and insertText events sequentially in iOS Safari

OS: iOS 17.0 · Device: iPhone or iPad Any · Browser: Safari 17.0

Open case →

Related Scenarios

Other scenarios that share similar tags or category.

Tags: ime, composition, input, ios, safari

Missing composition events on iOS (IME)

On some iOS Safari versions and keyboards, compositionstart or compositionupdate may not fire reliably for certain languages, while input events still fire—editors that only reconcile on composition boundaries can desync.

1 case

Tags: ime, beforeinput, input, ios, safari

iOS dictation triggers duplicate input events after completion

On iOS, when using voice dictation to input text into contenteditable elements, the system may fire duplicate beforeinput and input events after the initial dictation completes. The text is split into words and events are re-fired, causing synchronization issues. Composition events do not fire during dictation, making it difficult to distinguish dictation from keyboard input.

1 case

Tags: ime, composition, beforeinput, input

beforeinput and input events have different inputType values

During IME composition or in certain browser/IME combinations, the beforeinput event may have a different inputType than the corresponding input event. For example, beforeinput may fire with insertCompositionText while input fires with deleteContentBackward. This mismatch can cause handlers to misinterpret the actual DOM change and requires storing beforeinput's targetRanges for use in input event handling.

1 case

Tags: ime, composition, beforeinput, input

Selection mismatch between beforeinput and input events

The selection (window.getSelection()) in beforeinput events can differ from the selection in corresponding input events. This mismatch can occur during IME composition, text prediction, or when typing adjacent to formatted elements like links. The selection in beforeinput may include adjacent formatted text, while input selection reflects the final cursor position.

1 case

Tags: ime, composition, beforeinput, android

getTargetRanges() returns empty array in beforeinput events

The getTargetRanges() method in beforeinput events may return an empty array or undefined in various scenarios, including text prediction, certain IME compositions, or specific browser/device combinations. When getTargetRanges() is unavailable, developers must rely on window.getSelection() as a fallback, but this may be less accurate.

1 case

Comments & Discussion

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