[][src]Crate wasm_run

Rust Latest Version Docs.rs LOC Dependency Status License


Build tool that replaces cargo run to build WASM projects. Just like webpack, wasm-run offers a great deal of customization.

To build your WASM project you normally need an external tool like wasm-bindgen, wasm-pack or cargo-wasm. wasm-run takes a different approach: it's a library that you install as a dependency to a binary of your project. Because of that you don't need any external tool, the tooling is built as part of your dependences.

To build your project for production you can use the command cargo run -- build and to run a development server that reloads automatically when the sources change you can use cargo run -- serve.

Please note that there is a space between -- and build and between -- and serve!

One of the main advantage of this library is that it provides greater customization: you can set a few hooks during the build process in order to customize the build directory or use a template to generate your index.html, download some CSS, ... you name it. I personally use it to reduce the amount of files by bundling the CSS and the JS into the index.html so I had only two files (index.html, app_bg.wasm).


There are two basic examples to help you get started quickly:

  • a "basic" example for a frontend only app that rebuilds the app when a file change is detected;
  • a "backend-and-frontend" example using the web framework Rocket (backend) which uses Rocket itself to serve the file during the development (any file change is also detected and it rebuilds and restart automatically).


All the details about the hooks can be find on the macro main.

Additional Information

  • You can use this library to build examples in the examples/ directory of your project. cargo run --example your_example -- serve. But you will need to specify the name of the WASM crate in your project and it must be present in the workspace. Please check the "example" example.
  • If you want to use your own backend you will need to disable the serve feature by disabling the default features. You can use the full-restart feature to force the backend to also be recompiled when a file changes (otherwise only the frontend is re-compiled). You will also need to specify run_server to the macro arguments to run your backend.
  • You can add commands to the CLI by adding variants in the enum.
  • You can add parameters to the Build and Serve commands by overriding them. Please check the documentation on the macro main.
  • If you run cargo run -- serve --profiling, the WASM will be optimized.


  • prebuilt-wasm-opt: if you disable the default features and enable this feature, a binary of wasm-opt will be downloaded from GitHub and used to optimize the WASM. By default, wasm-opt is compiled among the dependencies (binaryen). This is useful if you run into troubles for building binaryen-sys. (binaryen cannot be built on Netlify at the moment.)
  • sass: support for SASS and SCSS. All SASS and SCSS files found in the directories styles/, assets/, sass/ and css/ will be automatically transpiled to CSS and placed in the build directory. This can be configured by overriding: [BuildArgs::build_sass_from_dir], [BuildArgs::sass_lookup_directories], [BuildArgs::sass_options] or completely overriden in the Hooks::post_build hook. sass-rs is re-exported in the prelude of wasm-run for this purpose.
  • full-restart: when this feature is active, the command is entirely restarted when changes are detected when serving files for development (cargo run -- serve). This is useful with custom serve command that uses a custom backend and if you need to detect changes in the backend code itself.



The wasm-run Prelude



A cargo child process.


Build arguments.


Serve arguments.





A build profile for the WASM.



A trait that allows overriding the build command.


An extension for Package and for Metadata to run a cargo command a bit more easily. Ideal for scripting.


A trait that allows overriding the serve command.

Attribute Macros


Makes an entrypoint to your binary (not WASM).