mahoraga-js

WebAssembly bindings for the mahoraga expression language, built for bundlers (Vite, webpack).

npm install mahoraga-js

import { evaluate } from "mahoraga-js";

evaluate("1 + 2 * 5");                                          // 11
evaluate("user.name | to_uppercase()", { user: { name: "ann" } }); // "ANN"
evaluate("price | discount(10)", { price: 50, discount: (p, pct) => p * (1 - pct / 100) }); // 45

try {
  evaluate("'test' + 2");
} catch (err) {
  // err.name: "LexerError" | "ParserError" | "EvalError"
  console.log(err.message, err.span, err.help);
}

Vite 8 loads the .wasm without plugins, but the dev server's dependency pre-bundling must skip the package. Otherwise the wasm and its JS glue end up as separate module instances and loading fails with wasm is undefined:

// vite.config.js
export default defineConfig({
  optimizeDeps: { exclude: ["mahoraga-js"] },
});

webpack 5 needs experiments: { asyncWebAssembly: true }. Node 24+ can import it directly, with an experimental-feature warning.

API

evaluate(expr, context?, maxLength = 2000) evaluates expr against the standard library. Keys of context become top-level identifiers.

| JS | mahoraga | |--------------------------------------|----------| | null | null | | undefined | void | | boolean | bool | | number (safe integer) | integer | | number (otherwise) | float | | bigint (fits in i64) | integer | | string | string | | plain object (or null prototype) | object | | Array | array | | function | closure |

Errors

Development

cargo install wasm-pack
wasm-pack build --release --target bundler                     # pkg/, the npm package
wasm-pack build --release --target nodejs --out-dir target/pkg-node
node --test 'tests/*.test.mjs'

Publishing

rm -rf pkg && wasm-pack build --release --target bundler
# On a clean build wasm-pack copies the license files but leaves them out of `files`.
npm pkg set 'files[]=LICENSE-MIT' --prefix pkg
npm publish ./pkg