fix(core): reopened first heading shows at body text size by YousefED · Pull Request #3193 · TypeCellOS/BlockNote

YousefED · 2026-10-14T07:19:09Z

Summary

When a collaborative document opens and its first block is a heading, the heading shows at body text size. It gets the correct size only after the user clicks in the editor.

This PR fixes the problem.

Closes #3013

Cause

The editor starts with a placeholder paragraph that has the id initialBlockId.
If the first edit changes this paragraph into a heading, the stored heading keeps this id.
When the document opens again, y-sync replaces the placeholder with the stored content. It does this in its plugin view, while the editor mounts.
PreviousBlockType finds the same id on both sides. Thus it marks the replacement as a paragraph to heading change and sets data-prev-type="paragraph".
Usually the plugin view of PreviousBlockType removes this attribute after one tick. But this view did not exist yet, so the attribute stayed until the next transaction.
With data-prev-type="paragraph", no heading size rule applies.

Change

PreviousBlockType does not mark block changes before its plugin view exists. Before that time, nothing is on the screen, so there is nothing to animate from. The heading now has the correct size at the first render, without an animation.

Testing

A new unit test in PreviousBlockType.test.ts adds a plugin view that changes a block's type while the editor mounts. The test fails without the fix and passes with it.

Summary by CodeRabbit

Bug Fixes
- Corrected block-type change handling when the editor view is being created. Headings are no longer incorrectly marked as updated or shown with a previous-type indicator after another extension changes their type.
- This keeps the displayed update state consistent with the content shown in the editor.

A plugin view that runs before PreviousBlockType's view can change a block's type while the editor mounts. y-sync does this on first render. Then the block kept data-prev-type until the next transaction, so a reopened first heading showed at body size until a click (#3013).

vercel · 2026-10-14T07:19:15Z

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coderabbitai · 2026-10-14T07:20:41Z

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between ce806b1 and aedc5c4.

📒 Files selected for processing: 2

packages/core/src/extensions/PreviousBlockType/PreviousBlockType.test.ts
packages/core/src/extensions/PreviousBlockType/PreviousBlockType.ts

Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 9 remain after this review.

📝 Walkthrough

The extension now tracks whether its ProseMirror view exists and skips document-change processing when it does not. A regression test covers an earlier plugin changing the initial paragraph to a heading during view creation.

Changes: Previous block type initialization

Layer / File(s)	Summary
View lifecycle guard and regression coverage `packages/core/src/extensions/PreviousBlockType/PreviousBlockType.ts`, `packages/core/src/extensions/PreviousBlockType/PreviousBlockType.test.ts`	The extension sets and clears a view-existence flag and skips document-change processing when no view exists. The regression test checks that a heading changed during view creation is not marked as updated and has no `[data-prev-type]` element.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: nperez0111

Merge Risk: ⚪ Minimal · up to aedc5

The mounting-time heading regression is covered by the new test. No actionable merge risk remains after normal checks.

Pre-merge checks: 5

Passed checks: 5 passed

Check name	Status	Explanation
Title check		The title clearly identifies the core fix: preventing the first reopened heading from rendering at body text size.
Description check		The description is mostly complete and directly related to the change. It explains the symptom, cause, implementation, linked issue, and regression test. It does not include every template section, bu…
Linked Issues check		Issue `#3013` requires correct first-paint heading size when collaboration replaces the `initialBlockId` placeholder, and removal of the stale transition state. `PreviousBlockTypeExtension` now skips do…
Out of Scope Changes check		The pull request changes only `PreviousBlockTypeExtension` and its regression test. The `hasView` guard directly supports the collaboration bootstrap rendering fix. The test verifies the reported fail…
Docstring Coverage		No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 2…

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_{A rabbit watched the heading rise,
No stale marker caught its eyes.
The view appeared; the guard stood by,
The first block kept its proper size.
Then off the rabbit hopped nearby.}

_{Comment @coderabbitai help to get the list of available commands.}

pkg-pr-new · 2026-10-14T07:22:55Z

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commit: aedc5c4

github-actions · 2026-10-14T07:25:09Z

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🚀 View preview at https://TypeCellOS.github.io/BlockNote/pr-preview/pr-3193/
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YousefED merged commit 8d1d50e into main Oct 14, 2026
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YousefED deleted the fix/previous-block-type-before-view branch October 14, 2026 07:25

YousefED mentioned this pull request Oct 15, 2026

⬆️(frontend) update BlockNote preview packages to 83153fda2e TypeCellOS/docs#12

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fix(core): reopened first heading shows at body text size - #3193

fix(core): reopened first heading shows at body text size#3193
YousefED merged 1 commit into
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fix/previous-block-type-before-view

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YousefED commented Oct 14, 2026 •

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