wassemble is a JavaScript tool to convert WebAssembly standard textual format (wat) to binary (wasm). It is a single file of JavaScript with no dependencies.

Note, wabt is a more full-featured toolkit for working with WebAssembly, both in textual and binary formats, and includes a tool called wat2wasm. However sometimes you just want a simple JS file to drop into your projects; that's what wassemble is about. You could think of it as a clone of wabt's wat2wasm, but built in a different way.

Unlike wat2wasm, wassemble does minimal error-checking. Notably, it doesn't type-check the module; it assumes the WebAssembly implementation will signal any validation-time errors when the module is instantiated. As such, this tool is most useful for compiling known-valid wat files, or for generating known-invalid modules for fuzzing or testing purposes.

npm install wassemble

As this project has no dependencies, alternately you can just drop wassemble.mjs anywhere in your project tree.

Assuming you installed via NPM, this code compiles a WebAssembly add function, synchronously instantiates it, and adds a couple numbers:

import wassemble from 'wassemble/wassemble.mjs';

let bytes = wassemble(`
  (module
    (func $add (export "add") (param i32 i32) (result i32)
      (i32.add (local.get 0) (local.get 1))))`)

let mod = new WebAssembly.Instance(new WebAssembly.Module(bytes));

console.log(mod.exports.add(10, 32));

Of course it's better to use WebAssembly.instantiate if possible.

wassemble is available under the Blue Oak Model License, version 1.0.0. See LICENSE.md for full details.