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Adding host functions for jco transpile

This folder contains a component that uses the wasi:logging interface with a custom host function for jco transpile.

This is a node CLI and browser based example implementation of running a component that imports the logging interface from a JavaScript application.

It uses jco to:

  • Generate a WebAssembly component (jco componentize) that can be executed anywhere WebAssembly components run
  • Generate JavaScript bindings (jco transpile) that execute the core functionality (in browser or compliant JS runtimes like NodeJS)

For another example of using jco with components in multiple environments, see the [jco example][docs-jco-example].

Component Interface

This component implements a simple WebAssembly Interface Types ("WIT") interface:

package example:host-logging@0.1.0;

@since(version = 0.1.0)
interface log-characters {
    call: func(s: string);
}

world component {
    import wasi:logging/logging@0.1.0-draft;

    export log-characters;
}

A component that implements the component world exports a single interface called log-characters, which consists of one function called call, which takes a string and outputs each character on a new line using the log-host.js host function.

Note

You can read more about the WIT syntax online.

Quickstart

Dependencies

First, install required dependencies:

npm install

Note

As this is a regular NodeJS project, you can use your package manager of choice (e.g. yarn, pnpm)

At this point, since this project is just NodeJS, you could use the module from any NodeJS project or browser project where appropriate.

That said, we'll be focusing on building the JS code we've written so far into a WebAssembly binary, which can run anywhere WebAssembly runtimes are supported, including in other languages, and the browser.

Building the WebAssembly binary

We can build a WebAssembly binary out of this JS project with jco:

npm run build

A WebAssembly binary will be written to component.wasm.

Running the binary in NodeJS via transpilation

While somewhat redundant in this JS-native context, we can use our produced WebAssembly binary (which could be written in any programming language) from JS projects with jco.

The process we want jco to perform for us is "transpilation" -- converting a WebAssembly binary into a JS module that can be run on any JS runtime that supports WebAssembly:

npm run transpile

Transpilation produces files in dist/transpiled that enable the WebAssembly component (component.wasm) to run in any compliant JS runtime.

With this transpiled module available, we can now run native JS code uses the WebAssembly module:

npm run transpiled-js

See run-transpiled.js for the full code listing.