What is Fable?

Fable is a compiler that lets you use F# to build applications that run in the JavaScript ecosystem.

type Shape =
    | Square of side: double
    | Rectangle of width: double * length: double

let getArea shape =
    match shape with
    | Square side -> side * side
    | Rectangle (width, length) -> width * length

let square = Square 2.0
printfn $"The area of the square is {getArea square}"

What is F#?#

F# (pronounced f-sharp) is a strongly typed Functional programming language which offers many great features to build robust and maintable code such as:

• Lightweight syntax
• Immutability baked into the language by default
• Rich types which let you represent easily your data or your domain
• Powerful pattern matching to define complex behaviors
• And so much more...

F# is already used on the server for web and cloud apps, and it's also used quite a lot for data science and machine learning. It's a great general-purpose language, and also a great fit for building beautiful UIs that run in the browser.

Why use F# for your next JavaScript project?#

F# is a great choice to build beautiful apps that run in the browser. F# is:

• Succinct with lightweight syntax
• Robust with a great type system and pattern matching
• Safe with immutability baked into the language
• Supported by large companies (such as Microsoft and Jetbrains) and comes with commercial tooling support

When compared with JavaScript, F# is safer, more robust, and more pleasant to read and write.

F# is a mature language with functional programming and object programming capabilities, but it doesn't sacrifice readability or simplicity to offer these things. Because of that, we think it's a great choice for your next JavaScript application.