watr

Light & fast WAT compiler

• feature & spec-complete, zero deps
• compile · polyfill · optimize · parse · prettify · minify
• instant wasm, JS interop, CLI, clear errors

docs  ·  demo

Usage

import watr, { compile, parse, print } from 'watr'

// compile to binary
const binary = compile('(func (export "f") (result f64) (f64.const 1))', {
  polyfill: false, // transform newer features to MVP
  optimize: true   // fold constants, treeshake, eliminate dead code ...
})
const module = new WebAssembly.Module(binary)
const { f } = new WebAssembly.Instance(module).exports

// parse
parse('(i32.const 42)') // ['i32.const', 42]

// print
print('(module(func(result i32)i32.const 42))') // (module\n  (func (result i32)\n  ...

// instant wasm function
const { add } = watr`(func (export "add") (param i32 i32) (result i32)
  (i32.add (local.get 0) (local.get 1))
)`
add(2, 3) // 5

// instant wasm: interpolate, auto-import ...
const { test } = watr`(func (export "test") (call ${console.log} (i32.const 42)))`
test() // logs 42

CLI

npx watr input.wat              # → input.wasm
npx watr input.wat -o out.wasm  # custom output
npx watr input.wat --print      # pretty-print
npx watr input.wat --minify     # minify
npx watr input.wat --optimize   # fold, treeshake, deadcode
npx watr input.wat --polyfill   # newer features → MVP

Metrics

• watr — 10 KB, 4,460 op/s
• spec/wast.js — 216 KB, 2,185 op/s
• wabt — 282 KB, 1,273 op/s
• binaryen — 1,100 KB, 718 op/s
• wat-compiler — 7.7 KB (MVP), 539 op/s

Used by

• jz – minimal static JS subset