Fable 5.0.0-rc.7
dotnet tool install --global Fable --version 5.0.0-rc.7
dotnet new tool-manifest
dotnet tool install --local Fable --version 5.0.0-rc.7
#tool dotnet:?package=Fable&version=5.0.0-rc.7&prerelease
nuke :add-package Fable --version 5.0.0-rc.7
Fable: F# |> JS
Fable is an F# to JavaScript compiler powered FSharp Compiler Services, designed to make F# a first-class citizen of the JavaScript ecosystem. Check the website for more information and if you find the project useful, don't forget to give us a star!
Fable actually uses a fork of FCS with a few tweaks. Binaries are in
lib/fcsfolder. See this PR for more info.
Getting started
Check this page.
Building
Requirements
Use VSCode Dev Container
You can use VSCode Dev Container to get a preconfigured environment both with requirements and VSCode extensions.
- You need to have docker installed and running.
- Install the Dev Container extension in VSCode
- Open the project in VSCode and click on the green button in the bottom left corner.
Use your machine
Make sure the following requirements are installed in your system:
- dotnet SDK 6 or higher
- node.js with npm
- Python 3 is installed and available as
python - Uv
- Rust
- Dart
- Erlang/OTP with rebar3 (for Beam/Erlang target)
Build
Run ./build.sh or ./build.cmd to see the build options.
When using VSCode, you can also run the build tasks from the command palette (Ctrl+Shift+P) by typing Run Task and selecting the task you want to run.
We also configured several debug configurations that you can use from the debug panel (Ctrl+Shift+D). This is useful as you can attach the debugger to the Fable compiler process to check what's going on.
Contributing
Just by using Fable you're already contributing! You can help the community a lot by sharing examples and experiences in your personal (or Fable's) blog and/or by editing the Fable Resources page.
Send bug reports (ideally with minimal code to reproduce the problem) and feature requests to this GitHub repository. To interact with the community you can use the Gitter chat but please note maintainers are not checking the chat regularly.
If you are up to contribute a fix or a feature yourself, you're more than welcome! Please send first an issue or a minimal Work In Progess PR so we can discuss the implementation details in advance.
List of changelogs
| Product | Versions Compatible and additional computed target framework versions. |
|---|---|
| .NET | net10.0 is compatible. net10.0-android was computed. net10.0-browser was computed. net10.0-ios was computed. net10.0-maccatalyst was computed. net10.0-macos was computed. net10.0-tvos was computed. net10.0-windows was computed. |
This package has no dependencies.
| Version | Downloads | Last Updated |
|---|---|---|
| 5.0.0-rc.7 | 96 | 4/7/2026 |
| 5.0.0-rc.6 | 235 | 3/31/2026 |
| 5.0.0-rc.5 | 1,304 | 3/20/2026 |
| 5.0.0-rc.4 | 108 | 3/19/2026 |
| 5.0.0-rc.3 | 574 | 3/10/2026 |
| 5.0.0-rc.2 | 273 | 3/3/2026 |
| 5.0.0-rc.1 | 216 | 2/26/2026 |
| 5.0.0-alpha.24 | 1,296 | 2/13/2026 |
| 5.0.0-alpha.23 | 518 | 2/3/2026 |
| 5.0.0-alpha.22 | 3,433 | 12/26/2025 |
| 5.0.0-alpha.21 | 2,679 | 12/15/2025 |
| 5.0.0-alpha.20 | 1,223 | 12/8/2025 |
| 5.0.0-alpha.19 | 603 | 12/4/2025 |
| 5.0.0-alpha.18 | 753 | 12/3/2025 |
| 5.0.0-alpha.17 | 798 | 11/27/2025 |
| 5.0.0-alpha.16 | 210 | 11/25/2025 |
| 5.0.0-alpha.15 | 1,283 | 11/19/2025 |
| 4.29.0 | 6,931 | 2/13/2026 |
| 4.28.0 | 8,773 | 11/25/2025 |
| 4.27.0 | 7,577 | 11/13/2025 |
### Added
* [Python/Beam] Add F# quotation support — construction, pattern matching, and evaluation via `LeafExpressionConverter.EvaluateQuotation` (by @dbrattli)
* [JS/TS] Add F# quotation support — construction, pattern matching, and evaluation (by @OnurGumus)
* [All] Add support for `Guid.CreateVersion7()` and `Guid.CreateVersion7(DateTimeOffset)` (by @OnurGumus)
* [All] Add missing `Array`, `List`, and `Seq` random choice/shuffle/sample members and tests (by @ncave)
* [Dart/Rust] Add missing `System.Random` implementations and tests (by @ncave)
* [Beam] Implement missing DateTimeOffset members, add DateOnly and TimeOnly support (by @dbrattli)
### Fixed
* [All] Fix unnecessary object allocations during AST traversal when visiting `Import` expressions (by Repo Assist)
* [Beam] Fix `System.Random.Next(0)` implementation (by @ncave)
* [Python] Fix `System.Random` seeded implementation (by @ncave)
* [Beam] Fix `System.Random` seeded implementation to use per-instance state (by @dbrattli)
* [Dart] Fix `Array.compareWith` comparing lengths before elements, producing wrong results for arrays with common prefixes (fixes #2961)
* [Python] Fix unsafe option unwrapping in `DateTimeOffset.get_Offset` and regex replacements (by @dbrattli)
* [All] Replace unsafe option `.Value` unwrapping with safe alternatives in Python/Replacements.fs and Rust/Fable2Rust.fs (code scanning alerts IONIDE-006)
* [All] Add `[<return: Struct>]` to partial active patterns in Dart and Rust targets to reduce allocations (code scanning alerts IONIDE-009)
* [JS/TS] Fix `Guid` to use cryptographically strong random values (by @ncave)
* [Python] Fix `DateTimeOffset` millisecond constructor and property (by @ncave)
* [Python] Implement missing `DateTimeOffset` members and fix equality/comparison to use UTC-normalized instants (by @dbrattli)
* [Python] Add `DateOnly` and `TimeOnly` support (by @dbrattli)
* [Python] Fix `String.IndexOf`/`LastIndexOf` with `StringComparison` argument emitting it as a start-index instead of a compile error (by @repo-assist)
* [Beam] Fix `String.IndexOf`/`LastIndexOf` with `StringComparison` argument incorrectly treating the enum value as a start index
* [JS/TS/Python] Fix `Async.StartChild` with timeout always timing out even when the computation finishes before the deadline (fixes #4481) (by @MangelMaxime)