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A cargo subcommand for the client-side Web

This cargo subcommand aims to make it easy and convenient to build, develop and deploy client-side Web applications written in Rust.

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This software was brought to you thanks to these wonderful people:

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Features

Currently it supports the following features:

It's also highly recommended that you check out the stdweb crate if you want to interact with the JavaScript world in your project. (In fact, cargo-web is what makes it possible to use stdweb's js! macro on Rust's native WebAssembly backend.)

Installation

$ cargo install cargo-web

To upgrade:

$ cargo install --force cargo-web

Or clone and build with $ cargo build --release then place in your $PATH.

On Linux the installation can fail with a message that it can't find OpenSSL, in which case you most likely need to install the -dev package for OpenSSL from your distribution's repositories. (On Ubuntu it's called libssl-dev.)

Web.toml

cargo-web has its own configuration file which you can put next to cargo's Cargo.toml.

Here's an example configuration showing every supported key:

# The default value of `--target` used when building this crate
# in cases where it's not specified on the command line.
default-target = "wasm32-unknown-unknown"

# This will prepend a given JavaScript file to the resulting `.js` artifact.
# You can put any initialization code here which you'd like to have executed
# when your `.js` file first loads.
#
# This accepts either a string (as shown here), or an array of strings,
# in which case it will prepend all of the specified files in their
# order of appearance.
prepend-js = "src/runtime.js"

[cargo-web]
# Asserts the minimum required version of `cargo-web` necessary
# to compile this crate; supported since 0.6.0.
minimum-version = "0.6.0"

# These will only take effect on *-emscripten targets.
[target.emscripten]
# You can have a target-specific `prepend-js` key.
prepend-js = "src/emscripten_runtime.js"
# This will enable Emscripten's SDL2 port. Consult Emscripten's documentation
# for more details.
link-args = ["-s", "USE_SDL=2"]

# You can also specify the target by its full name.
[target.wasm32-unknown-unknown]
prepend-js = "src/native_runtime.js"

If you use any external crates which have a Web.toml then cargo-web will load it and use it.

A few restrictions concerning the Web.toml:

Static files

Any static files you'd like to have served when running cargo web start or deployed when running cargo web deploy can be put in a directory called static in the root of your crate. No static artifacts are required by default; an index.html file will be automatically generated for you if it's missing. You can, of course, put your own static/index.html file, in which case it will be used instead of the autogenerated one.

Detecting cargo-web during compilation

If during compilation you'd like to detect that your project is being built with cargo-web you can check the COMPILING_UNDER_CARGO_WEB environment variable, which will be set to 1.

Using cargo-web on Travis

Precompiled binaries

You can use the following script to download and install the latest cargo-web:

CARGO_WEB_RELEASE=$(curl -L -s -H 'Accept: application/json' https://github.com/koute/cargo-web/releases/latest)
CARGO_WEB_VERSION=$(echo $CARGO_WEB_RELEASE | sed -e 's/.*"tag_name":"\([^"]*\)".*/\1/')
if [ "$(uname -s)" == "Darwin" ]; then
  CARGO_WEB_HOST_TRIPLE="x86_64-apple-darwin"
else
  CARGO_WEB_HOST_TRIPLE="x86_64-unknown-linux-gnu"
fi
CARGO_WEB_URL="https://github.com/koute/cargo-web/releases/download/$CARGO_WEB_VERSION/cargo-web-$CARGO_WEB_HOST_TRIPLE.gz"


echo "Downloading cargo-web from: $CARGO_WEB_URL"
curl -L $CARGO_WEB_URL | gzip -d > cargo-web
chmod +x cargo-web

mkdir -p ~/.cargo/bin
mv cargo-web ~/.cargo/bin

Running tests under headless Chrome

By default cargo web test will run your tests under headless Chrome. To be able to use this on Travis you need to add something like this to your .travis.yml:

addons:
  chrome: stable

Custom runtime (wasm32-unknown-unknown-only)

When building a project by default cargo-web generates a standalone runtime runtime for you. What this means is that the .js file which is generated can be immediately put inside of a <script> tag or launched with Node.js without having to load it manually or do anything extra, however this does limit you when it comes to customizability.

If you'd like to have a little more control on how your module is loaded then you can tell cargo-web to generate a non-standalone, library-like module for you with the --runtime library-es6 option. This will result in a .js file which exports a factory function with the following interface:

export default function() {
    return {
        imports: { ... },
        initialize: function( instance ) { ... }
    };
}

Here you have to instantiate the WebAssembly module yourself; in this case you have to pass imports as its imports, and then immediately after instantiating it call initialize.

For example, assuming you'll name your module generated by the cargo-web as my-module.mjs and my-module.wasm you can instantiate it like this from Node.js:

import fs from "fs";
import factory from "my-module.mjs";

// We read in the `.wasm` module.
const bytecode = fs.readFileSync( "my-module.wasm" );
const wasm = new WebAssembly.Module( bytecode );

// We instantiate it.
const instance = factory();
const compiled = new WebAssembly.Instance( wasm, instance.imports );

// This will initialize the module and call your `main`, if you have one.
const exports = instance.initialize( compiled );

// In the object it returns you can find any functions which
// you've exported with `stdweb`'s `#[js_export]` macro.
console.log( exports.add( 1, 2 ) );

Then you can run it with node --experimental-modules run.mjs.

This is useful if you want to load your .wasm file from a custom URL or you want to integrate the output with a JavaScript bundler, or anything else which requires you to load the module yourself.

Changelog

License

Licensed under either of

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.