@momiji-rs/sasso

sasso — a pure-Rust SCSS → CSS compiler (a dart-sass alternative) — as a tiny, dependency-free WebAssembly module. No wasm-bindgen, no native add-ons: one small .wasm plus a hand-written loader, so it runs the same in Node and the browser.

npm install @momiji-rs/sasso

import { compile } from "@momiji-rs/sasso";

const css = compile(`
  $brand: #2a7ae2;
  .button {
    color: $brand;
    &:hover { color: darken($brand, 10%); }
  }
`);
console.log(css);

// compressed output
compile("a { color: #ffffff }", { style: "compressed" }); // a{color:#fff}

compile(scss, options?) returns the CSS string, or throws an Error with the compiler's message on a Sass error. Options: { style?: "expanded" | "compressed" }.

Two builds: size vs speed

The default import is the size-optimized build (-Oz, ~350 KB gzip). For ~2× compile throughput on a larger module (~610 KB gzip), import the speed-optimized build instead — same API, same output:

import { compile } from "@momiji-rs/sasso";        // default: smallest module
import { compile } from "@momiji-rs/sasso/speed";  // ~2x faster, larger module

Tuning the bump-arena allocator

Both builds bump-allocate a single compile from a reusable arena region, which is the bulk of the speed advantage. The region defaults to 32 MiB of wasm linear memory (grown once on the first compile, then reused). Tune or disable it with configure() — before the first compile():

import { configure, compile } from "@momiji-rs/sasso/speed";

configure({ arenaMiB: 16 }); // smaller footprint (enough for typical sheets)
// configure({ arenaMiB: 0 }); // disable the arena: lowest memory, slower
compile(scss);

A stylesheet larger than the arena spills to the system allocator with no loss of correctness — just less speedup. The compile-time default is also settable when building from source: SASSO_WASM_ARENA_MB=16 bash wasm/build.sh.

For the CLI and the Rust library, see the main repository.

Licensed under MIT OR Apache-2.0.