cargo-web 0.6.14

A Cargo subcommand for the client-side Web
cargo-web-0.6.14 is not a library.

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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:

  • Daniel Norman
  • Anselm Eickhoff
  • Edward Knyshov
  • Ferran Pujol Camins
  • Johan Andersson
  • Stephen Sugden

Thank you!


Currently it supports the following features:

  • cargo web build - will build your project using one of Rust's three Web backends:
    • asm.js using Emscripten (when you pass --target=asmjs-unknown-emscripten; default)
    • WebAssembly using Emscripten (when you pass --target=wasm32-unknown-emscripten)
    • WebAssembly using Rust's native WebAssembly backend (when you pass --target=wasm32-unknown-unknown, requires Rust nightly)
  • cargo web test - will run your tests either under:
    • Under a headless instance of Google Chrome (default)
    • Under Node.js (when you pass --nodejs)
  • cargo web start - will build your project, start an embedded webserver and will continuously rebuild it if necessary; supports automatic reloading with --auto-reload.
  • cargo web deploy - will build your project and emit all of the necessary files so that you can easily serve them statically.
  • Will automatically download and install Emscripten for you (if necessary) on the following platforms:
    • Linux x86-64
    • Linux x86
  • Will automatically garbage-collect your WebAssembly artifacts.

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.)


$ 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.)


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"

# 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.
# 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.
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:

  • You can't have overlapping prepend-js keys. You can either define a single global prepend-js, or multiple per-target ones.
  • The link-args currently can't have any spaces in them.
  • The order in which cargo-web will process the Web.toml files from multiple crates is deterministic yet unspecified. This means that you shouldn't depend on this order in any way.

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=$(curl -L -s -H 'Accept: application/json'
CARGO_WEB_VERSION=$(echo $CARGO_WEB_RELEASE | sed -e 's/.*"tag_name":"\([^"]*\)".*/\1/')

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:

  chrome: stable


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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.