libqalculate-lite-wasm

libqalculate compiled to WebAssembly, exposing calculate(expression, timeoutMs) with plain-text output plus the library's exchange-rate feeds. A trimmed fork of stephtr/libqalculate-wasm for use inside the unimo desktop launcher, where every platform's webview runs the same wasm and no native libqalculate build is needed.

Usage

import loadLibqalculate from 'libqalculate-lite-wasm';
import wasmUrl from 'libqalculate-lite-wasm/dist/libqalculate.wasm?url'; // vite

const calc = await loadLibqalculate({ locateFile: () => wasmUrl });
const { expression, result, messages } = calc.calculate('2^10', 300);
// expression: "2^10", result: "1024", messages: []

An unknown name is reported in messages as an error. The deadline is cooperative and covers evaluation only: parsing is not interruptible, a hit deadline is not reported (the result is then partial, unevaluated, or the literal timed out), and thousands of nested calls throw. Keep inputs short.

The loader is built for the web (fetch); in Node or bun pass the bytes instead:

const calc = await loadLibqalculate({ wasmBinary: await Bun.file('.../libqalculate.wasm').arrayBuffer() });

Under a Content Security Policy, script-src needs 'wasm-unsafe-eval'.

dist/libqalculate.wasm.br is the same wasm brotli-compressed (about a quarter of the size). Serve it with Content-Encoding: br where you control the headers; otherwise decompress it in the page, e.g. with brotli-wasm:

import loadLibqalculate from 'libqalculate-lite-wasm';
import brotliPromise from 'brotli-wasm';
import wasmBrUrl from 'libqalculate-lite-wasm/dist/libqalculate.wasm.br?url'; // vite

const [brotli, compressed] = await Promise.all([brotliPromise, fetch(wasmBrUrl).then(r => r.arrayBuffer())]);
const calc = await loadLibqalculate({ wasmBinary: brotli.decompress(new Uint8Array(compressed)) });

Exchange rates

Currencies work immediately from the ECB snapshot that libqalculate embeds at its release; results carry a warning once those rates are more than a week old. For live rates the host fetches libqalculate's own feed files and hands the bodies over:

feed	source	body
1	European Central Bank, EUR base, about 30 currencies	eurofxref-daily.xml
2	Coinbase spot price of BTC in EUR	JSON with amount and currency
3	extra currencies (mycurrency.net, floatrates or currency-api layouts)	JSON

for (const feed of [1, 2, 3] as const) {
  const body = await (await fetch(calc.exchangeRatesUrl(feed))).text(); // or your own proxy
  calc.setExchangeRates(feed, body);
}

The bodies live in the module's in-memory filesystem, so the host keeps them (and their fetch time) and feeds them again after every load, refetching when older than a day. Inside a webview the fetch is subject to CORS; do it from the host process or through a proxy. Pass the bodies through untouched: libqalculate's XML walk depends on the whitespace between the ECB file's elements, so a proxy that re-serialises or minifies it silently yields no rates.

Consumed as a git dependency pinned to a commit; dist/ is tracked, so a consumer never needs the toolchain.

Building

toolchain.sh installs emsdk and builds GMP, MPFR, libxml2 and libqalculate for wasm (versions pinned at its top); compile.sh turns src/libqalculate.cc into dist/libqalculate.js + dist/libqalculate.wasm, plus dist/libqalculate.wasm.br for hosts that can serve the wasm with Content-Encoding: br. Locally, ./build-wasm.sh runs both through Docker (the daemon must be running; the first image build takes a while, each toolchain step is its own layer, and any edit to toolchain.sh rebuilds them all). CI runs the same two scripts in a node:22-bookworm container on every push, tests the committed dist/ first, caches the built libraries until toolchain.sh changes, tests the fresh build, and uploads it.

Commit dist/ with the source change that produced it; bun test runs a smoke check against it.

Defaults set in src/libqalculate.cc: radians, an unknown word is an error rather than a product of one-letter units, 10 significant digits, and ASCII operators, no digit grouping and no 0.333... so a copied result pastes anywhere.

Differences from upstream

• libqalculate pinned to a release tarball instead of git master.
• Single calculate() returning plain text; no set_option, variables or plot data.
• Exchange rates through libqalculate's own feed files (ECB, Coinbase BTC, extra currencies) instead of a JS rate table limited to EUR pairs.
• ES module output with typed locateFile / wasmBinary options.
• Built artifacts tracked in dist/, no npm publishing; Forgejo CI instead of GitHub Actions and a registry.

License

GPL-3.0-only, as upstream. libqalculate itself is GPL-2.0-or-later.