Typed character is duplicated when replacing a selection (single block or cross-block)

[wiebkevogel]

When text is selected (either within a single block or across multiple blocks) and a character is typed to replace the selection, the typed character appears twice instead of once (e.g. typing "a" results in "aa").

Steps to reproduce:

1. Go to the Editor.js playground (https://editorjs.io/)
2. Type some text into a block, e.g. "Hello world"
3. Select the block(s) with the mouse so they become highlighted (works when selecting a single block, and also when dragging the selection across multiple blocks)
4. Type a single character, e.g. "a"

Expected behavior:

The selected text is removed and replaced by the single typed character ("a").

Screencast:

Bildschirmaufnahme.2026-07-09.um.10.39.06.mov

Device, Browser, OS:

• Browser: Chrome (latest)
• OS: macOS 26.5.2
• Reproducible on official playground: Yes

Editor.js version:

• Version: 2.31.6

[waterWang]

Submitted PR #3016 with a fix for this issue.

Root cause: When blocks are selected and a printable key is typed, clearSelection removes the selected blocks and programmatically inserts the character via Caret.insertContentAtCaretPosition. However, event.preventDefault() was not called, so the browser also inserted the character at the caret position, resulting in the character appearing twice.

Fix: Added preventDefault() when the editor handles the character insertion itself, preventing the duplicate insertion.