# Undo and Redo

This page explains how `editorHistory` records editing state and how `undo()` / `redo()` restore the content and the caret.

## What Is Recorded

Each entry is a snapshot, not a diff:

| Field | Content |
|---|---|
| `index` | Row of the caret (0-based) |
| `offset` | Caret position within that row |
| `content` | `innerText` of every `<div>` row joined with `\n` |

Undo and redo are plain arrays with no size limit; continuous editing of a long document grows memory linearly with the number of steps.

## When Entries Are Written

| Action | Timing |
|---|---|
| `init()` (on construction and `clear()`) | Initial state written immediately |
| Normal typing (`input` event) | Delayed 300 ms; typing again cancels the previous timer, so a burst of typing becomes one entry |
| Cut, paste, Enter, Backspace, Tab, `Cmd/Ctrl+]` | Written via a 0 ms timer |
| Formatting methods (`bold()`, `heading()`, ...) | Written via a 0 ms timer |

Every write clears the redo stack, so any edit after an undo makes redo unavailable.

## undo()

1. Takes the second-to-last undo entry as the target; does nothing when fewer than two entries exist
2. Moves the last entry onto the redo stack
3. Calls `init(content, false, false)` with the target's `content` to rebuild the rows without recording
4. Puts the caret back at the target's `index` / `offset`
5. Updates the preview when `autosave` is truthy

## redo()

Pops the last redo entry, pushes it back onto the undo stack, then rebuilds, restores the caret and updates the preview just like `undo()`.

## Shortcuts

| Combo | Method |
|---|---|
| `Cmd/Ctrl+Z` | `undo()` |
| `Cmd/Ctrl+Shift+Z` | `redo()` |

Both work even with `hotKey: false`. `goBack()` and `goForward()` are the old names; see [Deprecations](/deprecations).