Rollup plugin for bundling and importing Rust crates.

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Rollup plugin for bundling and importing Rust crates.
This plugin internally uses wasm-bindgen.
wasm-bindgen is automatically installed, you do not need to install it separately.


First, make sure that rustup is installed.
If you are on Windows, then you also need to install the Visual Studio build tools (make sure to enable the "C++ build tools" option).
Lastly, run this:
yarn add --dev @wasm-tool/rollup-plugin-rust

Or if you're using npm you can use this instead:
npm install --save-dev @wasm-tool/rollup-plugin-rust


Add the plugin to your rollup.config.js, and now you can use Cargo.toml files as entries:
import rust from "@wasm-tool/rollup-plugin-rust";

export default {
    input: {
        foo: "Cargo.toml",
    plugins: [

You can import as many different Cargo.toml files as you want, each one will be compiled separately.
When compiling multiple crates it is recommended to use a single shared workspace to improve compile times.

Importing Cargo.toml within .js

It is also possible to import a Cargo.toml file inside of a .js file, like this:
import wasm from "./path/to/Cargo.toml";

async function loadWasm() {
    const exports = await wasm();

    // Use functions which were exported from Rust...

This will load the Rust .js glue code synchronously, but the Rust .wasm code will be loaded asynchronously (which is why the wasm function returns a Promise).
If you instead want to load everything asynchronously, you can use dynamic import, like this:
async function loadWasm() {
    const wasm = await import("./path/to/Cargo.toml");
    const exports = await wasm.default();

    // Use functions which were exported from Rust...

Customizing the import URL

At build time you can use the serverPath or importHook build options (described below) to customize the import URL for the .wasm file.
However, sometimes you need to customize the URL at runtime. In that case you can pass the serverPath or importHook options to the function (they behave the same as the build options):
import wasm from "./path/to/Cargo.toml";

async function loadWasm() {
    const exports = await wasm({
        // This will replace the directory with `/foo/`
        serverPath: "/foo/",

        // This will prepend `/bar/` to the import URL.
        importHook: (path) => "/bar/" + path

    // Use functions which were exported from Rust...

Usually you only need to pass one or the other, not both. Use serverPath for replacing the entire directory, and use importHook for prepending or doing more advanced things.

Build options

The default options are good for most use cases, so you generally shouldn't need to change them.
These are the default options:
    // Directory on your server where the .wasm files will be loaded from.
    // This is prepended to the URL, so you should put a / at the end of the directory,
    // for example "/foo/".
    serverPath: "",

    // Whether the code will be run in Node.js or not.
    // This is needed because Node.js does not support `fetch`.
    nodejs: false,

    // Whether to build in debug mode or release mode.
    // In watch mode this defaults to true.
    debug: false,

    // Whether to display extra compilation information in the console.
    verbose: false,

    // Whether to inline the `.wasm` file into the `.js` file.
    // This is slower and it increases the file size by ~33%,
    // but it does not require a separate `.wasm` file.
    // If this is `true` then `serverPath`, `nodejs`,
    // and `importHook` will be ignored.
    inlineWasm: false,

    // Extra arguments passed to `cargo build`.
    cargoArgs: [],

    // Extra arguments passed to `wasm-bindgen`.
    wasmBindgenArgs: [],

    // Arguments passed to `wasm-opt`.
    wasmOptArgs: ["-O"],

    // Which files it should watch in watch mode. This is relative to the Cargo.toml file.
    // Supports all of the glob syntax: https://www.npmjs.com/package/glob
    watchPatterns: ["src/**"],

    // Allows you to customize the behavior for loading the .wasm file,
    // this is for advanced users only!
    importHook: function (path) { return JSON.stringify(path); },

    // These options should not be relied upon, they can change or disappear in future versions.
    experimental: {
        // Changes the way that the modules are generated. Normally you import Rust like this:
        //     import wasm from "./path/to/Cargo.toml";
        //     async function loadWasm() {
        //         const exports = await wasm();
        //         // Use functions which were exported from Rust...
        //     }
        // But now you import Rust like this:
        //     import { foo, bar } from "./path/to/Cargo.toml";
        //     // Use functions which were exported from Rust...
        // You might need to set the Rollup `format` to "es" or "system".
        directExports: false,

        // Whether the Wasm will be initialized synchronously or not.
        // In the browser you can only use synchronous loading inside of Workers.
        // This requires `inlineWasm: true`.
        synchronous: false,

Chrome / Firefox extensions

If you are creating a Chrome / Firefox extension you may need to use importHook to customize the loading behavior, like this:
    importHook: function (path) {
        return "chrome.runtime.getURL(" + JSON.stringify(path) + ")";

This is necessary because extension files are put into a separate URL namespace, so you must use chrome.runtime.getURL to get the correct URL.

Environment variables

You can use the following environment variables to customize some aspects of this plugin:
  • CARGO_BIN is the path to the cargo executable.
  • WASM_BINDGEN_BIN is the path to the wasm-bindgen executable.
  • WASM_OPT_BIN is the path to the wasm-opt executable.

If not specified, they will use a good default value, so you shouldn't need to change them, this is for advanced uses only.