npm package: @fluidframework/undo-redo
Description: Undo Redo
Author: Microsoft and contributors
Latest version: 2.92.0

# @fluidframework/undo-redo

This package provides an implementation of an in-memory undo redo stack, as well as handlers for the SharedMap and
SharedSegmentSequence distributed data structures.

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## Using Fluid Framework libraries

When taking a dependency on a Fluid Framework library's public APIs, we recommend using a `^` (caret) version range, such as `^1.3.4`.
While Fluid Framework libraries may use different ranges with interdependencies between other Fluid Framework libraries,
library consumers should always prefer `^`.

If using any of Fluid Framework's unstable APIs (for example, its `beta` APIs), we recommend using a more constrained version range, such as `~`.

## Installation

To get started, install the package by running the following command:

```bash
npm i @fluidframework/undo-redo
```

## API Documentation

API documentation for **@fluidframework/undo-redo** is available at <https://fluidframework.com/docs/apis/undo-redo>.

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## Undo Redo Stack Manager

The undo redo stack manager is where undo and redo commands are issued, and it holds the stack of all undoable and
redoable operations. The undo redo stack manager is a stack of stacks.

The outer stack contains operations, and the inner stack contains all the IRevertible objects that make up that
operation. This allows the consumer of the undo redo stack manager to determine the granularity of what is undone or
redone.

For instance, you could define a text operation at the word level, so as a user types you could close the current
operation whenever the user types a space. By doing this when the user issues an undo mid-word the characters typed
since the last space would be undone, if they issue another undo the previous word would then be undone.

As mentioned above, operations are a stack of IRevertible objects. As suggested by the name, these objects have the
ability to revert some change which usually means two things. They must be able to track what was changed, and store
enough metadata to revert that change.

In order to create IRevertible object there are provided undo redo handlers for commonly used data structures.

## Shared Map Undo Redo Handler

The SharedMapUndoRedoHandler generates IRevertible objects, SharedMapRevertible for all local changes made to a SharedMap and pushes them to the current operation on the undo redo stack. These objects are created via the valueChanged event of the SharedMap. This handler will never close the current operation on the stack. This is a fairly simple handler, and a good example to look at for understanding how IRevertible objects should work.

## Shared Segment Sequence Undo Redo Handler

The SharedSegmentSequenceUndoRedoHandler generates IRevertible objects, SharedSegmentSequenceRevertible for any
SharedSegmentSequence based distributed data structures like SharedString.

This handler pushes an SharedSegmentSequenceRevertible for every local Insert, Remove, and Annotate operations made to
the sequence. The objects are created via the sequenceDelta event of the sequence. Like the SharedMapUndoRedoHandler
this handler will never close the current operation on the stack.

This handler is more complex than the SharedMapUndoRedoHandler. The handler itself batches the SharedSegmentSequence
changes into the smallest number of IRevertible objects it can to minimize the memory and performance overhead on the
SharedSegmentSequence of tracking changes for revert.

### Shared Segment Sequence Revertible

The SharedSegmentSequenceRevertible does the heavy lifting of tracking and reverting changes on the underlying
SharedSegmentSequence. This is accomplished via TrackingGroup objects. A TrackingGroup creates a bi-direction link
between itself and the segment. This link is maintained across segment movement, splits, merges, and removal. When a
sequence delta event is fired the segments contained in that event are added to a TrackingGroup. The TrackingGroup is
then tracked along with additional metadata, like the delta type and the annotate property changes. From the
TrackingGroup's segments we can find the ranges in the current document that were affected by the original change even
in the presence of other changes. The segments also contain the content which can be used. With the ranges, content,
and metadata we can revert the original change on the sequence.

As called out above, there is some memory and performance overhead associated with undo redo. This overhead is from the
TrackingGroup. This overhead manifests in a few ways:

-   Removed segments in a TrackingGroup will not be garbage collected from the backing tree structure.
-   Segments can only be merged if they have all the same TrackingGroups.

This object minimizes the number of TrackingGroups created, so this overhead is very low. This undo redo infrastructure
is entirely in-memory so it does not affect other users or sessions. If custom IRevertible objects use TrackingGroups
this overhead should be kept in mind to avoid possible performance issues.

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## Minimum Client Requirements

These are the platform requirements for the current version of Fluid Framework Client Packages.
These requirements err on the side of being too strict since within a major version they can be relaxed over time, but not made stricter.
For Long Term Support (LTS) versions this can require supporting these platforms for several years.

It is likely that other configurations will work, but they are not supported: if they stop working, we do not consider that a bug.
If you would benefit from support for something not listed here, file an issue and the product team will evaluate your request.
When making such a request please include if the configuration already works (and thus the request is just that it becomes officially supported), or if changes are required to get it working.

### Supported Runtimes

-   NodeJs ^20.10.0 except that we will drop support for it [when NodeJs 20 loses its upstream support on 2026-04-30](https://github.com/nodejs/release#release-schedule), and will support a newer LTS version of NodeJS (22) at least 1 year before 20 is end-of-life. This same policy applies to NodeJS 22 when it is end of life (2027-04-30).
    -   Running Fluid in a Node.js environment with the `--no-experimental-fetch` flag is not supported.
-   Modern browsers supporting the es2022 standard library: in response to asks we can add explicit support for using babel to polyfill to target specific standards or runtimes (meaning we can avoid/remove use of things that don't polyfill robustly, but otherwise target modern standards).

### Supported Tools

-   TypeScript 5.4:
    -   All [`strict`](https://www.typescriptlang.org/tsconfig) options are supported.
    -   [`strictNullChecks`](https://www.typescriptlang.org/tsconfig) is required.
    -   [Configuration options deprecated in 5.0](https://github.com/microsoft/TypeScript/issues/51909) are not supported.
    -   `exactOptionalPropertyTypes` is currently not fully supported.
        If used, narrowing members of Fluid Framework types types using `in`, `Reflect.has`, `Object.hasOwn` or `Object.prototype.hasOwnProperty` should be avoided as they may incorrectly exclude `undefined` from the possible values in some cases.
-   [webpack](https://webpack.js.org/) 5
    -   We are not intending to be prescriptive about what bundler to use.
        Other bundlers which can handle ES Modules should work, but webpack is the only one we actively test.

### Module Resolution

[`Node16`, `NodeNext`, or `Bundler`](https://www.typescriptlang.org/tsconfig#moduleResolution) resolution should be used with TypeScript compilerOptions to follow the [Node.js v12+ ESM Resolution and Loading algorithm](https://nodejs.github.io/nodejs.dev/en/api/v20/esm/#resolution-and-loading-algorithm).
Node10 resolution is not supported as it does not support Fluid Framework's API structuring pattern that is used to distinguish stable APIs from those that are in development.

### Module Formats

-   ES Modules:
    ES Modules are the preferred way to consume our client packages (including in NodeJs) and consuming our client packages from ES Modules is fully supported.
-   CommonJs:
    Consuming our client packages as CommonJs is supported only in NodeJS and only for the cases listed below.
    This is done to accommodate some workflows without good ES Module support.
    If you have a workflow you would like included in this list, file an issue.
    Once this list of workflows motivating CommonJS support is empty, we may drop support for CommonJS one year after notice of the change is posted here.

    -   Testing with Jest (which lacks [stable ESM support](https://jestjs.io/docs/ecmascript-modules) due to [unstable APIs in NodeJs](https://github.com/nodejs/node/issues/37648))

## Contribution Guidelines

There are many ways to [contribute](https://github.com/microsoft/FluidFramework/blob/main/CONTRIBUTING.md) to Fluid.

-   Participate in Q&A in our [GitHub Discussions](https://github.com/microsoft/FluidFramework/discussions).
-   [Submit bugs](https://github.com/microsoft/FluidFramework/issues) and help us verify fixes as they are checked in.
-   Review the [source code changes](https://github.com/microsoft/FluidFramework/pulls).
-   [Contribute bug fixes](https://github.com/microsoft/FluidFramework/blob/main/CONTRIBUTING.md).

Detailed instructions for working in the repo can be found in the [Wiki](https://github.com/microsoft/FluidFramework/wiki).

This project has adopted the [Microsoft Open Source Code of Conduct](https://opensource.microsoft.com/codeofconduct/).
For more information see the [Code of Conduct FAQ](https://opensource.microsoft.com/codeofconduct/faq/) or contact [opencode@microsoft.com](mailto:opencode@microsoft.com) with any additional questions or comments.

This project may contain Microsoft trademarks or logos for Microsoft projects, products, or services.
Use of these trademarks or logos must follow Microsoft’s [Trademark & Brand Guidelines](https://www.microsoft.com/trademarks).
Use of Microsoft trademarks or logos in modified versions of this project must not cause confusion or imply Microsoft sponsorship.

## Help

Not finding what you're looking for in this README? Check out [fluidframework.com](https://fluidframework.com/docs/).

Still not finding what you're looking for? Please [file an issue](https://github.com/microsoft/FluidFramework/wiki/Submitting-Bugs-and-Feature-Requests).

Thank you!

## Trademark

This project may contain Microsoft trademarks or logos for Microsoft projects, products, or services.

Use of these trademarks or logos must follow Microsoft's [Trademark & Brand Guidelines](https://www.microsoft.com/en-us/legal/intellectualproperty/trademarks/usage/general).

Use of Microsoft trademarks or logos in modified versions of this project must not cause confusion or imply Microsoft sponsorship.

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