If you're open to Forth,

https://github.com/remko/waforth

> WAForth is entirely written in (raw) WebAssembly*, and the compiler generates WebAssembly code on the fly.

* https://github.com/remko/waforth/blob/master/src/waforth.wat

Ben Lynn's page https://crypto.stanford.edu/~blynn/compiler/ compiles (a large subset of) Haskell to web assembly (which you can download; a prime number sieve yielded 40KB of code) and runs it in the browser.

I'm working on a TypeScript/Swift/Dart style language, and currently this hello-world is 1444 bytes:

    export let main = () => {
      console.log("Hello, World!");
    };

I think it really helps to have a language designed from the ground-up to obsess over bytes for WASM. Trying to do that with a familiar high-level language with a rich standard library is tricky.

WebAssembly Text Format (wat) is fine to use. You declare functions that run imperative code over primitive i32/i64/f32/f64 values, and write to a block of memory. Many algorithms are easy enough to port, and LLMs are pretty great at generating wat now.

I made Orb as a DSL over raw WebAssembly in Elixir. This gives you extract niceties like |> piping, macros so you can add language features like arenas or tuples, and reusability of code in modules (you can even publish to the package manager Hex). By manipulating the raw WebAssembly instructions it lets you compile to kilobytes instead of megabytes. I’m tinkering on the project over at: https://github.com/RoyalIcing/Orb

> compiles to wasm in less than 1Mb of wasm

Janet, a Clojure-like Lisp compiles a whole playground of itself and the std lib in 823kb: https://janetdocs.org/playground

https://codeberg.org/veqq/janetdocs/src/branch/master/public...

you can do smaller for other things.

C based Mandelbrot WASM demos can be ~1 KB total. Assuming you mean a simple scripting language though, Assembly Script does exactly that.

you can just compile c/c++ to wasm in the browser - there are wasi/emscripten builds of clang itself around (yosys, clang-repl, etc).