ProseMirror: splitBlock crashes on specific node nesting

Phenomenon

In April 2025, a regression was identified in prosemirror-commands (fixed in v1. 6.2). When the splitBlock command was executed at the very end of a block that had a sibling in its parent, the logic for finding the split depth could miscalculate the document size, leading to a fatal RangeError. This effectively rendered the editor unusable for complex structured documents.

Reproduction Steps

1. Use prosemirror-commands between 1.6.0 and 1.6.1.
2. Create a document with a block (e.g., a paragraph) inside another block (e.g., a blockquote), followed by a sibling node.
3. Position the caret at the end of the inner paragraph.
4. Trigger the splitBlock command (e.g., press Enter).

Observed Behavior

• Crash: The browser console reports RangeError: Position out of range from within the ProseMirror library.
• View Freeze: The DOM is not updated, and further input may be blocked.

Expected Behavior

The inner block should be split into two, maintaining the parent’s structure.

References & Solutions

Mitigation: Upgrade Commands Package

This was a library-level logic error. The fix involved correcting the range calculation when splitting near document boundaries.

# Fix by upgrading to the latest version
npm update prosemirror-commands

• ProseMirror-commands v1.6.2 Release Notes
• ProseMirror GitHub Commit: fix(splitBlock) correctly calculate range