insertParagraph preventDefault breaks IME composition state in Safari

Overview

In Safari desktop, when a developer intercepts the insertParagraph action (typically triggered by pressing Enter) by calling preventDefault() in either the keydown or beforeinput event handler, the browser’s internal IME (Input Method Editor) composition state becomes corrupted. After this occurs, subsequent text input using IME (Korean, Japanese, Chinese, etc.) fails to work correctly. The input event may not fire properly, characters may not be inserted, or the composition state may remain in an inconsistent state.

Impact

• IME Input Failure: After preventing insertParagraph, IME input stops working correctly
• Missing Input Events: The input event may not fire for subsequent IME input
• Composition State Corruption: IME composition state becomes inconsistent
• Character Loss: Typed characters may not appear in the contenteditable element
• User Experience Degradation: Users cannot continue typing after Enter is prevented

Technical Details

The issue occurs when:

1. User is typing with IME (Korean, Japanese, Chinese, etc.) in a contenteditable element
2. User presses Enter key, which triggers insertParagraph
3. Developer calls preventDefault() in keydown or beforeinput event handler to prevent the paragraph insertion
4. Safari suppresses the default paragraph insertion behavior
5. However, Safari’s internal IME composition state management becomes corrupted
6. Subsequent IME input fails to trigger proper input events or insert characters correctly

Event Sequence

The problematic sequence:

1. keydown (Enter key) - if preventDefault() is called here
2. beforeinput (inputType: “insertParagraph”) - if preventDefault() is called here
3. IME composition state becomes corrupted
4. Next IME input attempt:
   • compositionstart may not fire
   • compositionupdate may not fire
   • input event may not fire
   • Characters may not be inserted

Browser Comparison

• Safari (Desktop): This issue occurs. Preventing insertParagraph breaks subsequent IME input
• Chrome: May have different behavior, needs verification
• Firefox: May have different behavior, needs verification
• Edge: May have different behavior, needs verification

Root Cause Analysis

According to research and WebKit bug reports:

1. Composition Event Overlap: When Enter is pressed during or after IME composition, Safari needs to handle both the paragraph insertion and composition state transitions. Preventing the paragraph insertion disrupts this coordination.

2. Internal State Mismatch: Safari’s internal IME state tracking becomes out of sync with the actual DOM state when insertParagraph is prevented, especially if there are formatting wrappers or empty nodes.

3. Event Ordering Issues: WebKit has known issues with event ordering around composition, where keydown that ends a composition session may fire after compositionend, or have incorrect isComposing values.

4. Non-cancelable Composition Events: Composition-related input events (insertCompositionText) are not cancelable per spec, but canceling insertParagraph may interfere with the composition lifecycle.

Workarounds

1. Check Composition State Before Preventing

Only prevent insertParagraph when not composing:

editor.addEventListener('beforeinput', (e) => {
  if (e.inputType === 'insertParagraph') {
    // Only prevent if not currently composing
    if (!e.isComposing) {
      e.preventDefault();
      // Custom paragraph insertion logic
    }
    // If composing, allow default behavior to maintain IME state
  }
});

2. Handle Enter in keydown with Composition Check

editor.addEventListener('keydown', (e) => {
  if (e.key === 'Enter' && !e.isComposing) {
    e.preventDefault();
    // Custom paragraph insertion
  }
  // If isComposing is true, let the default behavior proceed
});

3. Defer Custom Behavior Until After Composition

let isComposing = false;

editor.addEventListener('compositionstart', () => {
  isComposing = true;
});

editor.addEventListener('compositionend', () => {
  isComposing = false;
});

editor.addEventListener('beforeinput', (e) => {
  if (e.inputType === 'insertParagraph' && isComposing) {
    // Don't prevent during composition
    return;
  }
  if (e.inputType === 'insertParagraph') {
    e.preventDefault();
    // Custom logic
  }
});

4. Manual IME State Reset (Advanced)

If composition state is already corrupted, attempt to reset it:

function resetIMEState(editor) {
  // Blur and refocus to reset IME state
  editor.blur();
  setTimeout(() => {
    editor.focus();
    // Clear any lingering composition state
    const selection = window.getSelection();
    if (selection.rangeCount > 0) {
      selection.removeAllRanges();
      selection.addRange(selection.rangeCount === 0 ? 
        document.createRange() : selection.getRangeAt(0));
    }
  }, 0);
}

Related Cases

• Case IDs will be added as cases are created for specific environment combinations

References

• W3C Input Events Level 2 Specification - Official specification for insertParagraph inputType
• WebKit Blog: Enhanced Editing with Input Events - WebKit’s implementation details for beforeinput events
• ProseMirror Issue #944: Duplicated characters in Safari with IME - Related issue about IME composition state corruption in Safari
• WebKit Bug 269922: Add API to programmatically manipulate text composition - Request for better composition state control
• WebKit Bug 67763: Crashes in WebCore::InsertNodeBeforeCommand constructor - InsertParagraph command crash issues
• WebKit Mailing List: Caret/Predictive Text Bar out of sync - Selection changes during composition
• ProseMirror Discuss: IME composing problems in table cells - Safari IME composition issues