#document #less #minify #web #directory #core #cargo #javascript #serving


wasmdev core implementation, used by wasmdev server + macros

1 unstable release

0.1.7 Jul 7, 2023

#417 in WebAssembly

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61 downloads per month
Used in 3 crates (2 directly)

MIT license

107 lines


crates.io docs.rs

Simple web development for web frontends written in rust:

// src/main.rs
fn main() {
    let window = web_sys::window().unwrap();
    let document = window.document().unwrap();
    let body = document.body().unwrap();
    let val = document.create_element("p").unwrap();
    val.set_text_content(Some("Hello World"));
cargo run
Compiling my-web-app
 Finished dev [unoptimized + debuginfo] target(s)
  Running `target/debug/my-web-app`
 Building wasm target
Compiling my-web-app
 Finished dev [unoptimized + debuginfo] target(s)
  Serving ┃ ┃ <= Click to open your app!

Project Goal

wasmdev aims to provide the most simple way to develop your rust frontend web application. The idea is to use cargo just like you would do when developing a native/binary executable. No need to install tools like trunk or wasm-pack. Just add wasmdev to your dependencies and add a macro in front of your main function, and you have yourself a web server fit for rapid development! You can also build all web assets with a simple cargo build --release, and they will be minified and ready for distribution. How cool is that!


Note: Project is in early stage of development. Bugs or other problems might still be present, error messages might have a long way to go etc. Don't use for large or $$$ projects. Use more tested tools like trunk instead.

Note: The server application that is used to run and test your web frontend app is NOT suitable for hosting your web-app in a production environment. It lacks many common http server features and is only intended to be a fast and simple way to test and develop your web frontend app.

Note: Since the web server and the web front-end is the same application, changing the front-end code will cause cargo to recompile the server part of the application as well every time you run cargo build. When a project grows, this might become a big bottleneck. When a project is large enough, cargo wasmdev can be installed and used instead of wasmdev macro. This command provides the same features, but will remove the extra compilation time of building the web server.


What wasmdev DO:

wasmdev has similar features as trunk. Like:

  • Auto-recompile and reload on rust/wasm on code changes
  • Hot-reload on static file changes (like css-styles)

It also has some features that trunk don't have (I believe), like:

  • Optimized and minified release builds without additional tools or processes:
    • Run cargo build --release and you have your dist-optimized assets
  • Auto-setup of console_error_panic_hook in your frontend app (can be disabled)

What wasmdev DOESN'T DO:

  • Server side rendering
  • Transpilation of javascript to adhere to a certain ECMAScript version
  • Bundle multiple javascript files together
  • No sass or less. Might be implemented in the future as optional features


The following options can be set to wasmdev::main macro:

  • addr: Socket address to webserver
    • Default ""
  • path: Path to static web assets
    • Default: "src"
  • port: TCP socket port to use
    • Default: 8080
  • watch: Reload assets on file-system changes
    • Default: true
    • Note: Only affects debug build, always false for release build
// src/main.rs
#[wasmdev::main(port: 8080, path: "src")]
fn main() {

Use-case: index.html override

By default, all files in src folder is served by the web server. You can add your index.html file here to override the default one. This is necessary to pull in additional assets like css styles.

<!doctype html>
    <head><link rel="stylesheet" href="/index.css"></head>

Project file-tree:

├── Cargo.toml
└── src
    ├── index.css
    ├── index.html
    └── main.rs

Use-case: override asset path:

If you want to have a separate path to static assets, they can be specified in the wasmdev::main macro as mention previously. This is recommended, since the web-server won't try to recompile your wasm-code when you change your static assets.

// src/main.rs
#[wasmdev::main(path: "www")]
fn main() {

Project file-tree:

├── Cargo.toml
├── src
│   └── main.rs
└── www
    └── index.html

Use-case: Don't include console_error_panic_hook

Just add wasmdev and ignore the default features:

cargo add wasmdev --no-default-features

Build release version for distribution:

When building your project with a release build, the web assets (all javascript files and wasm code) will be built and optimized for release.

cargo build --release
Compiling my-web-app
 Finished release [optimized] target(s)
 Finished release artifacts in: 'target/dist/my-web-app'
 Finished release [optimized] target(s)

The release artifacts will be located at target/dist/{project_name}

└── target
    └── dist
        └── my-web-app
            ├── index.html
            ├── index.js
            └── index.wasm

When building in release mode, cache invalidation of build artifacts might not always work. This can happen if:

  • You create a new static asset without modifying the rust source code or any existing static asset.

Changing any rust file in src directory, or pre-existing static asset fixes this.

Code examples

All examples can be built and executed by cargo like this:

cargo run -p <example>
# Run the simple project that outputs "Hello World"
cargo run -p simple

See examples folder for a complete list of examples.


  • MIT


  • Robin Grönberg


  • Write unit tests
  • Implement an easy way to run all tests (in the browser) by simply running cargo test with the test result in the cli window. Not sure if this is possible.

Ideas for further minification

The result is somewhat minimized but we can minimize it further (~10-15% improvement). So, go to target dir:

cd target/dist/<example>

This command will replace js/wasm glue code function names (in a hacky way) to minimized versions (requires wasm-opt):

../../../replace.sh index.js index.wasm

Install swc and minimize javascript one final time (requires node/npm)

npm install swc
npx swc index.js -C jsc.target=es2017 -C minify=true -C jsc.minify.compress=true -C jsc.minify.mangle=true -o index.js

Now, test your site with python http server (or similar):

python3 -m http.server 8080


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