Compiling to webassembly

At this stage RustPython only has preliminary support for web assembly. The instructions here are intended for developers or those wishing to run a toy example.

Setup

To get started, install wasm-pack and npm. (wasm-bindgen should be installed by wasm-pack. if not, install it yourself)

Build

Move into the wasm directory. This directory contains a library crate for interop with python to rust to js and back in wasm/lib, the demo website found at https://rustpython.github.io/demo in wasm/demo, and an example of how to use the crate as a library in one's own JS app in wasm/example.

cd wasm

Go to the demo directory. This is the best way of seeing the changes made to either the library or the JS demo, as the rustpython_wasm module is set to the global JS variable rp on the website.

cd demo

Now, start the webpack development server. It'll compile the crate and then the demo app. This will likely take a long time, both the wasm-pack portion and the webpack portion (from after it says "Your crate has been correctly compiled"), so be patient.

npm run dev

You can now open the webpage on https://localhost:8080 and Python code in either the text box or browser devtools with:

rp.pyEval(
    `
print(js_vars['a'] * 9)
`,
    {
        vars: {
            a: 9,
        },
    },
);

Alternatively, you can run npm run build to build the app once, without watching for changes, or npm run dist to build the app in release mode, both for the crate and webpack.

Updating the demo

If you wish to update the WebAssembly demo, open a pull request to merge main into the release branch. This will trigger a Travis build that updates the demo page.

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