Deploying Rust and WebAssembly

At this point in time deploying Rust and WebAssembly to the web or other locations unfortunately isn't a trivial task to do. This page hopes to serve as documentation for the various known options, and as always PRs are welcome to update this if it's out of date!

The methods of deployment and integration here are primarily tied to the --target flag.

Value Summary
bundler Suitable for loading in bundlers like Webpack
web Directly loadable in a web browser
nodejs Loadable via require as a Node.js module
deno Loadable using imports from Deno modules
no-modules Like web, but older and doesn't use ES modules


--target bundler

The default output of wasm-bindgen, or the bundler target, assumes a model where the wasm module itself is natively an ES module. This model, however, is not natively implemented in any JS implementation at this time. As a result, to consume the default output of wasm-bindgen you will need a bundler of some form.

Note: the choice of this default output was done to reflect the trends of the JS ecosystem. While tools other than bundlers don't support wasm files as native ES modules today they're all very much likely to in the future!

Currently the only known bundler known to be fully compatible with wasm-bindgen is webpack. Most examples use webpack, and you can check out the hello world example online to see the details of webpack configuration necessary.

Without a Bundler

--target web or --target no-modules

If you're not using a bundler but you're still running code in a web browser, wasm-bindgen still supports this! For this use case you'll want to use the --target web flag. You can check out a full example in the documentation, but the highlights of this output are:

  • When compiling you'll pass --target web to wasm-bindgen
  • The output can natively be included on a web page, and doesn't require any further postprocessing. The output is included as an ES module.
  • The --target web mode is not able to use NPM dependencies.
  • You'll want to review the browser requirements for wasm-bindgen because no polyfills will be available.

The CLI also supports an output mode called --target no-modules which is similar to the web target in that it requires manual initialization of the wasm and is intended to be included in web pages without any further postprocessing. See the without a bundler example for some more information about --target no-modules.


--target nodejs

If you're deploying WebAssembly into Node.js (perhaps as an alternative to a native module), then you'll want to pass the --target nodejs flag to wasm-bindgen.

Like the "without a bundler" strategy, this method of deployment does not require any further postprocessing. The generated JS shims can be require'd just like any other Node module (even the *_bg wasm file can be require'd as it has a JS shim generated as well).

Note that this method requires a version of Node.js with WebAssembly support, which is currently Node 8 and above.


--target deno

To deploy WebAssembly to Deno, use the --target deno flag. To then import your module inside deno, use

// @deno-types="./out/crate_name.d.ts"
import { yourFunction } from "./out/crate_name.js";


If you'd like to deploy compiled WebAssembly to NPM, then the tool for the job is wasm-pack. More information on this coming soon!