lexical_history 1.7.3

Undo and redo for lexical_core, built on immutable editor-state snapshots with deterministic, tag-driven coalescing. Pure Dart, no Flutter dependency.

lexical_history

Undo and redo for lexical_core. Pure Dart, no Flutter dependency.

Install

dependencies:
  lexical_history: ^1.0.0

Use

import 'package:lexical_core/lexical_core.dart';
import 'package:lexical_history/lexical_history.dart';

final editor = LexicalEditor();
final dispose = registerHistory(editor);

editor.dispatchCommand(undoCommand, null);
editor.dispatchCommand(redoCommand, null);
editor.dispatchCommand(clearHistoryCommand, null);

dispose();   // removes every registration

Observing availability, for a toolbar:

editor
  ..registerCommand(canUndoCommand, (canUndo) {
    setState(() => _canUndo = canUndo);
    return false;                    // observe without claiming the command
  }, CommandPriority.editor)
  ..registerCommand(canRedoCommand, (canRedo) {
    setState(() => _canRedo = canRedo);
    return false;
  }, CommandPriority.editor);

How it works

An undo stack is a list of EditorState references. That is not a shortcut — committed states are immutable and share every untouched node with their predecessor, so retaining one costs a pointer plus the nodes that actually changed. There is no operation log to replay and therefore no way for undo to drift from the document it claims to restore. Selection is part of the state, so it is restored for free.

Coalescing

The interesting design question is which consecutive edits share one undo entry. This package decides from update tags and the dirty-node set, never from a timer. Undo granularity then depends on what the user did rather than on how fast they typed, and the behaviour is deterministic enough to test — timer-based coalescing produces suites that pass locally and flake in CI.

A run continues only when all of the following hold:

• exactly one text node changed;
• its format, style and mode did not;
• no element was modified in its own right (the root is exempt — the transform pass always flags it, so its dirty state carries no information);
• the new text extends or truncates the old one at a single edge;
• the change is the same kind as the previous one, in the same node.

Anything else starts a new entry: a format toggle, a split, a paste, a structural change, or switching from typing to deleting.

Two tags override the decision:

Tag	Effect
historyPushTag (history-push)	Force a new undo entry
historyMergeTag (history-merge)	Fold into the current entry
historicTag (historic)	Applied by this package to its own state swaps, so undo does not record itself

editor.update(() { /* ... */ }, tags: {historyPushTag});

Bounding

HistoryState(maxDepth: 500) caps retained entries; the oldest are dropped first. Pass your own instance to inspect depth or to share one across editors.

Licence

MIT. Derived from Lexical, © Meta Platforms, Inc., also MIT. See NOTICE.