This package have a set of methods to handle a state history for an atom or a set of atoms. Useful for complex forms, WYSIWYG and so on.

Installation

npm i @reatom/undo

Usage

All methods reuse WithUndo interface which includes the following atoms and actions.

• jump action allows you to navigate entire history by passed index.
• undo action is a shortcut to jump(ctx, -1).
• redo action is a shortcut to jump(ctx, +1).
• clearHistory action clear the whole history.
• isUndoAtom atom with a boolean state which represent the current position (is it possible to do "undo").
• isRedoAtom atom with a boolean state which represent the current position (is it possible to do "redo").
• positionAtom atom with a number state which represent the index of current history position.
• historyAtom atom with a list of states, it could help you to know the size of the history. You shouldn't change it by yourself!

All methods accepts the optional properties:

• length is the max amount of state records, 30 by default
• shouldUpdate function allows you to ignore some updates, by default it skips state updates which is equal to the last history record
• shouldReplace function allows you define what to do with the new update, replace the last history record (true) or add a new record (false - by default)
• withPersist - WithPersist instance from one of the adapter of @reatom/persist. It will persist data from historyAtom and persistAtom, the target atom init state may be derived from the history, if it preserve.

withUndo

withUndo adds extra methods for an existing atom to handle the state history and navigate through it.

import { atom } from '@reatom/core'
import { withUndo } from '@reatom/undo'

const inputAtom = atom('').pipe(withUndo())

shouldReplace

Example: https://codesandbox.io/s/reatom-react-undo-7g2cwg?file=/src/App.tsx

This option helps you store only important updates by replacing the last state with the new one. It is useful when you need to store the fresh data but separate it into parts.

For example, we want to save in the history all user input, but the each record of the history should include only words, not a letters.

const inputAtom = atom('').pipe(
  withUndo({ shouldReplace: (ctx, state) => !state.endsWith(' ') }),
)

for (const letter of 'This is a test') {
  inputAtom(ctx, (s) => s + letter)
}
ctx.get(inputAtom) // 'This is a test'
ctx.get(inputAtom.historyAtom).length // 4

inputAtom.undo(ctx)
ctx.get(inputAtom) // 'This is a'

inputAtom.undo(ctx)
inputAtom.undo(ctx)
ctx.get(inputAtom) // 'This'

reatomUndo

reatomUndo creates a computed atom that collects the states of the passed atoms and manages them in a single history line. You can read the state of the resulting atom as a snapshot of all the states of the passed atoms.

The second argument accepts all withUndo options.

import { atom } from '@reatom/core'
import { reatomUndo } from '@reatom/undo'

const formUndoAtom = reatomUndo([emailAtom, passwordAtom], { length: 50 })

reatomDynamicUndo

reatomDynamicUndo accepts a callback to spy a dynamic list of atoms and manage their changes in a single history line. It is useful when you want to use atomization pattern. It is a more powerful version of reatomUndo, but it requires proper subscription to function correctly. Also, the state of this atom is not useful, do not read it.

The second argument accepts all withUndo options.

Example: https://codesandbox.io/s/reatom-react-atomization-undo-65rmfm?file=/src/model.ts