Deployment - The `wasm-bindgen` Guide

# 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hopes to serve as documentation for the various known options, and as always PRs are welcome to update this if it's out of date!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 CommonJS module
`deno` | Loadable using imports from Deno modules
`no-modules` | Like `web`, but older and doesn't use ES modules
`experimental-nodejs-module` | Loadable via `import` as a Node.js ESM module.

## Bundlers

`--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`.

## Node.js

`--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.

## Node.js Module

`--target experemintal-nodejs-module`

If you're deploying WebAssembly into Node.js as a JavaScript module, then you'll want to pass the `--target experimental-nodejs-module` flag to `wasm-bindgen`.

Like the "node" strategy, this method of deployment does not require any further postprocessing. The generated JS shims can be `import`ed just like any other Node module.

Note that this method requires a version of Node.js with WebAssembly and module support, which is currently Node 12 and above.

Currently experimental. Target is expected to be changed before stabilization.

## Deno

`--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";

## NPM

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!