Plain JS in, tiny WASM out. No rewrite, no runtime, no GC.
For DSP, math, visuals and more.
Hero demo compiling in your browser…
JZ compiles a distilled JavaScript subset, Crockford’s “good parts” – into native-grade WASM.
Valid JZ is valid JS. Same source runs as plain JS or compiles without rewrite to .wasm – sandboxed, portable, memory-safe. No runtime, no GC, no type annotations, auto-SIMD, deterministic output.
| Good for | Not for |
|---|---|
| DSP, audio, synthesis | UI, DOM, frontend state |
| Images, video, pixels | Network, hot I/O, serving HTTP |
| Simulation, physics, games | Dynamic object models and monkey-patching |
| Parsers, codecs, compression | Allocation-heavy, long-lived object graphs |
| Scientific, numeric, edge ML | Security-sensitive cryptography and arbitrary-precision integers |
| Hashing, checksums, RNG | Tiny calls where the JS/WASM boundary dominates |
A minimal modern functional JS subset – no dynamic constructs or reflection. The jzify layer lowers legacy patterns, generators, and async/await.
let x = 0.5, Float32Array, an array index, a loop counter. JZ infers it instead of turning the file into another language. Ambiguous values take a slower, always-correct dynamic path.Porffor aims to cover the full JS spec but emits no WASM (its 2026 rewrite compiles through C to native) and runs slower than V8 on the cases it completes; scriptc makes native CLI binaries from TypeScript, no WASM target; AssemblyScript is a typed TypeScript dialect for WASM whose source can’t run as JS.
JZ compiles plain JS that still runs and tests as JS, and the release gate keeps its WASM fastest per case; the price is the overdynamic constructs it refuses.
Rust, Go, and C are excellent when a rewrite and second toolchain make sense. JZ is for the hot path you want to keep in JavaScript: one source, one test suite, a JS fallback, and comparable WASM or native performance.
JZ leads V8 and AssemblyScript by geomean on the covered corpus and targets near-native speed. The release gate is stricter than an average: JZ must be the fastest WASM on every case. Per-case numbers, missing target coverage, and every measured loss stay visible on the bench page; a rival win remains a bug to close, not an exception to hide.
If you hit a slow case, report it →
WASM isn't magically faster – V8 also JIT-compiles hot JS to machine code. But a JIT pays for staying ready for any JS: shape checks, deopt guards, GC pauses in the hot loop. JZ's subset is closed, so it commits ahead of time to what a JIT only gambles on – static layout, monomorphic calls, no GC – and auto-vectorizes loops to SIMD, which V8 doesn't attempt on plain JS.
jz → wasm2c → clang -O3 produces a standalone native binary. See full pipeline →.
jz.wasm, and the self-compiled build passes the full test suite in CI. 
It’s experimental (pre-1.0) – ABI can still shift.
But real code already ships on it: color-space v3 builds its precompiled 27-space WASM backend with JZ.
CI gates the full suite, test262, the bench, and the self-compile. A fuzzer diffs every kernel against the same source in V8.
And the exit is free: valid JZ is valid JS – drop the compile step and the same file keeps running.
jz kernel.js) or the API (compile()) produces a plain .wasm you load like any other module. Setup & options →Find it useful?
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