emit

(From the book WebAssembly from the Ground Up — learn Wasm by building a simple compiler in JavaScript.)

A JavaScript library to emit WebAssembly 1.0 binary modules.

Installation

npm i @wasmgroundup/emit

Example

Build a WebAssembly module with an exported add function:

import * as w from "@wasmgroundup/emit";

const mod = w.module([
  w.typesec([w.functype([w.valtype.i32, w.valtype.i32], [w.valtype.i32])]),
  w.funcsec([w.typeidx(0)]),
  w.exportsec([w.export_("add", w.exportdesc.func(w.funcidx(0)))]),
  w.codesec([
    w.code(
      w.func(
        [],
        w.expr([
          [w.instr.local.get, ...w.i32(0)],
          [w.instr.local.get, ...w.i32(1)],
          w.instr.i32.add,
        ]),
      ),
    ),
  ]),
]);

const { instance } = await WebAssembly.instantiate(w.flatten(mod));
const { add } = instance.exports as { add: (a: number, b: number) => number };
console.log(add(1, 2)); // 3

Features

• Simple API following the spec's naming conventions
• Full support for WebAssembly 1.0 specification
• Generate binary WASM modules directly from JavaScript
• Zero dependencies

License

MIT (see LICENSE file)