npm package: @fluidframework/register-collection
Description: Consensus Register
Author: Microsoft and contributors
Latest version: 2.92.0

# @fluidframework/register-collection

A consensus register collection is a distributed data structure (DDS), which holds a set of registers and their versions generated during concurrent updates. In the simplest definition, two updates on a single register are concurrent if there is no causal relationship between them (i.e., neither knows about the other). On such cases of concurrent updates, a register internally stores all possible versions of a value.

<!-- AUTO-GENERATED-CONTENT:START (LIBRARY_README_HEADER) -->

<!-- prettier-ignore-start -->
<!-- NOTE: This section is automatically generated using @fluid-tools/markdown-magic. Do not update these generated contents directly. -->

## 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/register-collection
```

## Importing from this package

This package leverages [package.json exports](https://nodejs.org/api/packages.html#exports) to separate its APIs by support level.
For more information on the related support guarantees, see [API Support Levels](https://fluidframework.com/docs/build/releases-and-apitags/#api-support-levels).

To access the `public` ([SemVer](https://semver.org/)) APIs, import via `@fluidframework/register-collection` like normal.

To access the `legacy` APIs, import via `@fluidframework/register-collection/legacy`.

## API Documentation

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

<!-- prettier-ignore-end -->

<!-- AUTO-GENERATED-CONTENT:END -->

### Detecting concurrency in Fluid

In distributed systems literature, detecting concurrency requires some form of logical/physical clock. A popular technique used in replicated databases such as dynamodb is called version vectors where each key stores a collection of `[time, value]` tuples. `time` is essentially a reference clock used to decide concurrency amongst updates. Each update to a key includes the `time`, essentially to indicate how `caught up` the replica was during that update.

In Fluid, each operation contains a referenceSequenceNumber (`refSeq`), which essentially refers to how caught up the client was (in terms of sequence number) during that update. We can use this property to implement a similar concurrency model. Mathematically, if an update has a `refSeq N`, it can overwrite/discard any other prior values with `sequenceNumber (seq) <= N`. It is safe to do so because the client must have seen all those updates before posting its own update. Hence this update is not concurrent with those overwritten updates. However, the update is still concurrent with any other update with `seq > N`. Therefore those versions are still kept.

### Conflict resolution policies

Below are the policies that the DDS implements:

-   Versions: Returns all stored concurrent versions. App is responsible for conflict resolution. Amazon's shopping cart policy based on dynamodb is a popular example of this policy.

-   LWW: The last write to a key always overwrites any prior writes (aka last write win policy). This is exactly same as Fluid's Shared Map policy.

-   Atomic: The policy follows the same semantics of a shared distributed lock. Amongst all concurrent updates, only the first writer wins. In distributed systems literature, the register update policy is called `Atomic`. This behavior requires a linearizable register. A linearizable register behaves as if there is only a single copy of the data, and that every operation appears to take effect atomically at one point in time. This definition implies that operations are executed in an well-defined order. On a concurrent update, we perform a `compare-and-set` operation, where we compare a register's stored `seq` with the incoming `refSeq`. The earliest operation overwriting the stored `seq` wins since every client reaches to an agreement on the value. Hence we can safely return the first value.

<!-- AUTO-GENERATED-CONTENT:START (README_FOOTER) -->

<!-- prettier-ignore-start -->
<!-- NOTE: This section is automatically generated using @fluid-tools/markdown-magic. Do not update these generated contents directly. -->

## 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.

<!-- prettier-ignore-end -->

<!-- AUTO-GENERATED-CONTENT:END -->