Skip to content

These docs are for Miniflare 2 which is no longer supported apart from critical security updates.
Please see the migration guide to upgrade to Miniflare 3, and the updated API docs.

Visit Miniflare on GitHub
Set theme to dark (⇧+D)

⚙️ WebAssembly


WebAssembly modules are bound as follows. The bound keys will be instances of WebAssembly.Module:

$ miniflare --wasm MODULE1=module1.wasm --wasm MODULE2=module2.wasm
MODULE1 = "module1.wasm"
MODULE2 = "module2.wasm"
const mf = new Miniflare({
wasmBindings: {
MODULE1: "module1.wasm",
MODULE2: "module2.wasm",

You can then use the WebAssembly modules in your workers:

const instance = new WebAssembly.Instance(MODULE1);
addEventListener("fetch", (e) => {
// Assuming MODULE1 exports a function `add` summing 2 integer arguments
const value = instance.exports.add(1, 2);
e.respondWith(new Response(value.toString()));


You can also import WebAssembly modules by adding a CompiledWasm module rule. See 📚 Modules for more details. For instance, with the following wrangler.toml file and worker script, we can achieve the same result as the previous example:

type = "CompiledWasm"
globs = ["**/*.wasm"]
import module1 from "./module1.wasm";
const instance = new WebAssembly.Instance(module1);
export default {
fetch() {
const value = instance.exports.add(1, 2);
return new Response(value.toString());

Rust Wrangler Builds

When using Rust Wrangler Builds, wasm is automatically bound to your compiled WebAssembly module.