Fable 5.7.0
dotnet tool install --global Fable --version 5.7.0
dotnet new tool-manifest
dotnet tool install --local Fable --version 5.7.0
#tool dotnet:?package=Fable&version=5.7.0
nuke :add-package Fable --version 5.7.0
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 |
|---|---|---|
| 5.7.0 | 100 | 7/9/2026 |
| 5.6.0 | 571 | 7/5/2026 |
| 5.5.0 | 772 | 6/30/2026 |
| 5.4.0 | 1,049 | 6/24/2026 |
| 5.3.0 | 1,783 | 6/16/2026 |
| 5.2.0 | 1,458 | 6/11/2026 |
| 5.1.0 | 1,507 | 5/28/2026 |
| 5.0.0 | 21,582 | 4/21/2026 |
| 5.0.0-rc.7 | 1,039 | 4/7/2026 |
| 5.0.0-rc.6 | 387 | 3/31/2026 |
| 5.0.0-rc.5 | 1,780 | 3/20/2026 |
| 5.0.0-rc.4 | 169 | 3/19/2026 |
| 5.0.0-rc.3 | 1,023 | 3/10/2026 |
| 5.0.0-rc.2 | 413 | 3/3/2026 |
| 5.0.0-rc.1 | 334 | 2/26/2026 |
| 5.0.0-alpha.24 | 1,371 | 2/13/2026 |
| 5.0.0-alpha.23 | 724 | 2/3/2026 |
| 5.0.0-alpha.22 | 7,309 | 12/26/2025 |
| 5.0.0-alpha.21 | 4,555 | 12/15/2025 |
| 4.29.0 | 19,741 | 2/13/2026 |
### 🚀 Features
* Add `--noGitignore` flag to skip generating fable_modules/.gitignore (#4730) ([3742b950](https://github.com/fable-compiler/Fable/commit/3742b95070df0bd43abfe0c5a20609a790757651))
### 🐞 Bug Fixes
* MailboxProcessor dropping falsy messages and unit replies ([8299b2e7](https://github.com/fable-compiler/Fable/commit/8299b2e7f690e9136906653155883a08607aa4a4))
* *(all)* Include original exception message when loading a Fable plugin fails (#4739) ([659e73a4](https://github.com/fable-compiler/Fable/commit/659e73a4c59db397fb0821de371ea5c48731d505))
* *(all)* Add `Seq.enumerateTryWith` for try/with in seq, list, array comprehensions (#4750) ([448c90d7](https://github.com/fable-compiler/Fable/commit/448c90d7ccba80ee3d3c38432a2a1d1407f6dc69))
* *(beam)* EndsWith regression for empty pattern with non-ordinal comparison ([eee2ad3f](https://github.com/fable-compiler/Fable/commit/eee2ad3f09071fe3d924e3375f26897fd69753d2))
* *(js/ts)* Represent union cases with no fields as singletons ([3f6e618e](https://github.com/fable-compiler/Fable/commit/3f6e618eb33b7344437476dc5f2f7334a29662aa))
* *(js/ts)* Match .NET NaN semantics in JS comparison, min and max ([7e5106f9](https://github.com/fable-compiler/Fable/commit/7e5106f9d93cb55ae4aca4656868fa0c53493991))
* *(js/ts)* BigInteger byte-array corruption, checked conversions, gcd, log2 (#4743) ([f3cb7f2b](https://github.com/fable-compiler/Fable/commit/f3cb7f2bfc9e46e558763867d6c1ba323bcf281c))
* *(js/ts)* Observable/Event dropping null/undefined/unit values (#4742) ([75bff73b](https://github.com/fable-compiler/Fable/commit/75bff73be3743fe0af37f99c541b10f6978150f3))
* *(js/ts)* EndsWith regression for empty pattern with non-ordinal comparison ([7793ed7b](https://github.com/fable-compiler/Fable/commit/7793ed7b0fc1f33bf3da6c0ea31607e172726267))
* *(js/ts/python)* Quote strings with the %A format specifier (#4749) ([75321f3b](https://github.com/fable-compiler/Fable/commit/75321f3b2cb70ea345a0a45d6343cbb6e0de466f))
* *(python)* Accept native floats in fable-library float functions (#4724) ([ea4a9853](https://github.com/fable-compiler/Fable/commit/ea4a98531e1dc1c55b902bb00753018ae48a3de3))
* *(python)* Represent union cases with no fields as singletons ([0211b4cc](https://github.com/fable-compiler/Fable/commit/0211b4ccf19b4eb8ea4677a6734d7e691020cb68))
* *(python)* Emit forward reference for self-referencing static union members (#4752) ([452b85f2](https://github.com/fable-compiler/Fable/commit/452b85f26bcec34bfdc61405162948bf7d8810c0))
* *(python)* Match .NET NaN and signed-zero semantics in comparison, min and max ([383bb93c](https://github.com/fable-compiler/Fable/commit/383bb93ccd35e03dfaa1bbf897ef9ac83ae1ec95))
* *(python)* `LastIndexOf(value, startIndex)` off-by-one on inclusive boundary ([bad6bcac](https://github.com/fable-compiler/Fable/commit/bad6bcacf8d8d17337ae3bdb988da648f23c9640))
* *(python)* MailboxProcessor dropping unit replies ([8e83ebe3](https://github.com/fable-compiler/Fable/commit/8e83ebe3c676c02af2ff1c37199f5680d320cfb0))
* *(ts/js)* `Regex.Replace` count/substitutions and `Regex.Split` semantics (#4741) ([d6ae6bd3](https://github.com/fable-compiler/Fable/commit/d6ae6bd3790b57b31941a118cdffaeb6a59155c3))
### ⚡ Performance Improvements
* *(python)* Use native operators for int64/uint64 arithmetic (#4727) ([f062d668](https://github.com/fable-compiler/Fable/commit/f062d668f3514e5f43d5307e7504e7ca124efcce))
* *(python)* Rewrite hot Seq combinators as native Python generators (#4728) ([73e0eab9](https://github.com/fable-compiler/Fable/commit/73e0eab9c3071f44fd87da38658a8b73acfa3ccc))
* *(python)* Read union case fields directly instead of rebuilding Array (#4725) ([e4eaa80b](https://github.com/fable-compiler/Fable/commit/e4eaa80b1e9390abee0d2d53bcdb026a5633b7c6))
<strong><small>[View changes on Github](https://github.com/fable-compiler/Fable/compare/7f915f1dd66b9a5fbbd56f858b07d39b98519b65..d6ae6bd3790b57b31941a118cdffaeb6a59155c3)</small></strong>