Fable 5.5.0
dotnet tool install --global Fable --version 5.5.0
dotnet new tool-manifest
dotnet tool install --local Fable --version 5.5.0
#tool dotnet:?package=Fable&version=5.5.0
nuke :add-package Fable --version 5.5.0
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 |
|---|---|---|
| 5.5.0 | 106 | 6/30/2026 |
| 5.4.0 | 575 | 6/24/2026 |
| 5.3.0 | 1,643 | 6/16/2026 |
| 5.2.0 | 1,110 | 6/11/2026 |
| 5.1.0 | 1,416 | 5/28/2026 |
| 5.0.0 | 18,614 | 4/21/2026 |
| 5.0.0-rc.7 | 986 | 4/7/2026 |
| 5.0.0-rc.6 | 383 | 3/31/2026 |
| 5.0.0-rc.5 | 1,767 | 3/20/2026 |
| 5.0.0-rc.4 | 166 | 3/19/2026 |
| 5.0.0-rc.3 | 905 | 3/10/2026 |
| 5.0.0-rc.2 | 370 | 3/3/2026 |
| 5.0.0-rc.1 | 326 | 2/26/2026 |
| 5.0.0-alpha.24 | 1,361 | 2/13/2026 |
| 5.0.0-alpha.23 | 716 | 2/3/2026 |
| 5.0.0-alpha.22 | 6,834 | 12/26/2025 |
| 5.0.0-alpha.21 | 4,356 | 12/15/2025 |
| 5.0.0-alpha.20 | 1,602 | 12/8/2025 |
| 5.0.0-alpha.19 | 630 | 12/4/2025 |
| 4.29.0 | 19,338 | 2/13/2026 |
### 🚀 Features
* *(all)* Add `Compiler.is*` target detection flags for conditional branching (#4692) ([621dea31](https://github.com/fable-compiler/Fable/commit/621dea31daaef6a9dcf8a2ac5ceb144a063bb873))
* *(js/ts)* Map task { } to Promise<T> ([97f54d36](https://github.com/fable-compiler/Fable/commit/97f54d3692e5ba881c249b289c20b4fad5ac27e2))
* *(js/ts/python/beam)* Add support for `Async.AwaitEvent` (#4693) ([71c98179](https://github.com/fable-compiler/Fable/commit/71c981792b6ff99cd417bb2e70a13a9d55ed72cf))
### 🐞 Bug Fixes
* *(all)* Pass raw value for optional arguments of native bindings (#4688) ([a4c75483](https://github.com/fable-compiler/Fable/commit/a4c7548313fcbefc0ff0eddc7a95d8d0599d68a6))
* *(all)* Support .NET format specifiers and alignment in interpolated strings (#4695) ([7c50a3af](https://github.com/fable-compiler/Fable/commit/7c50a3af39aee935ce318f44e04247da32b33f0f))
* *(all)* Error on inline function referencing private value (#4701) ([cea6806e](https://github.com/fable-compiler/Fable/commit/cea6806ea388e73cf42fb673960f7862bb497fc2))
* *(beam)* Support module-level mutable variables via process dictionary (#4676) ([535b9af0](https://github.com/fable-compiler/Fable/commit/535b9af06969bcd7bdf118bdfb633ccadd5e4177))
* *(beam)* Namespace module-level mutable state keys by module (#4683) ([1ec28ab1](https://github.com/fable-compiler/Fable/commit/1ec28ab10923623eaf04b90bf8ffbeb54469d454))
* *(js)* Respect StringComparison in String.IndexOf/LastIndexOf (#4681) ([7cb92d52](https://github.com/fable-compiler/Fable/commit/7cb92d522e5dc8dfe51351565504c59a94c2f408))
* *(js/ts)* Implicit DateTime to DateTimeOffset conversion (#4697) ([fcbd9b91](https://github.com/fable-compiler/Fable/commit/fcbd9b91397a41226df4bed25c1bd1f0667efb64))
* *(js/ts)* Int list is not a union type (#4698) ([ecbecbe7](https://github.com/fable-compiler/Fable/commit/ecbecbe756610fd83a621c005e97eda92bbc332a))
* *(js/ts)* Hoist emitJsStatement imports with trailing comments (#4702) ([e820eb72](https://github.com/fable-compiler/Fable/commit/e820eb7239b2ffe0f2cb4bf3e6c040a1c7dca57f))
* *(js/ts)* Uncurry mutable module value alias calls (#4703) ([0de0d218](https://github.com/fable-compiler/Fable/commit/0de0d2187a68db0ac35bd2546dd98eb1c67397e5))
* *(js/ts)* Pass TypeInfo to getRecordFields to handle None fields in anonymous records (#4704) ([c977d78b](https://github.com/fable-compiler/Fable/commit/c977d78b39225a51c7bd051a1fe363ed0ccbe201))
* *(js/ts/python)* Drop allowAccessToPrivateRepresentation arg from reflection calls (#4689) ([ec3cded7](https://github.com/fable-compiler/Fable/commit/ec3cded78cc98dc740ce978d3bb078f2603f4846))
* *(python)* Fix task while loop stack overflow ([fdb0ec37](https://github.com/fable-compiler/Fable/commit/fdb0ec375e4464117470a528e427ee3df174f62a))
* *(ts)* Use declared type-param names in object expression generic methods (#4685) ([1c3e7d99](https://github.com/fable-compiler/Fable/commit/1c3e7d99653c7119c615b6dfd095a45e36add5b3))
* *(ts)* Use signature type-param names when implementing generic interface methods (#4686) ([03e5deee](https://github.com/fable-compiler/Fable/commit/03e5deeedaa35be2974f40e439e520526cf4c1ba))
* *(ts)* Bound enum-constrained type parameters with `extends number` (#4687) ([15daf624](https://github.com/fable-compiler/Fable/commit/15daf6245212ddb8b7ac6296631381711e34c98d))
* *(ts)* Widen isEnumDefined value parameter to accept any value (#4690) ([0d6498dd](https://github.com/fable-compiler/Fable/commit/0d6498ddf65e0e18918690633da23b04b78479f6))
* *(ts)* Keep enclosing type parameters in scope for nested members (#4691) ([f5723a2d](https://github.com/fable-compiler/Fable/commit/f5723a2d008408e1bca140256a452ac556c69c00))
* *(ts)* Re-declare class type params on generic static attached members (#4696) ([2da50780](https://github.com/fable-compiler/Fable/commit/2da50780b8254cfad05f3a645780f60999cae4ee))
* *(ts)* Filter class type params from attached let-binding methods (#4700) ([d3a6a1dd](https://github.com/fable-compiler/Fable/commit/d3a6a1dd09066b25d876e28446d70fea58162abd))
<strong><small>[View changes on Github](https://github.com/fable-compiler/Fable/compare/c9b3ee2429a4688946c1936e27df730837428070..c977d78b39225a51c7bd051a1fe363ed0ccbe201)</small></strong>