JavaScript

JavaScript can be used as a Tier 1 guest language.

The tools used in this guide are:

@bytecodealliance/jco - Convert Javascript to WASM Components
@bytecodealliance/componentize-js - JavaScript Componentization Tool

The easiest way to get started once the tooling is installed is to use the golem-cli new command as described in the Quickstart.

View the available examples with:

golem-cli list-examples --language javascript

Then generate a new example project with:

golem-cli new --example js-actor-minimal --component-name js-component

Manual Installation

Here's the target project structure

main.js

main.wit

package.json

Add a package.json file

package.json

{
  "type": "module",
  "scripts": {
    "build": "jco componentize -w wit -o out/component.wasm src/main.js"
  },
  "devDependencies": {
    "@bytecodealliance/componentize-js": "0.8.3",
    "@bytecodealliance/jco": "1.1.1"
  }
}

Create a WIT File

Create a WIT file in the wit directory, for example wit/main.wit:

 
package golem:component;
 
interface api {
  add: func(value: u64);
  get: func() -> u64;
}
 
world demo  {
  export api;
}

Create a main.js file

Create an empty main.js file in the src directory:

Full file path from the root of the project: src/main.js

The exported object must have the same shape as the interface exported by your WIT world.

let state = 0
 
export const api = {
  add(value) {
    console.log(`Adding ${value} to the counter`)
    state += Number(value)
  },
  get() {
    console.log(`Returning the current counter value: ${state}`)
    return BigInt(state)
  },
}

Install Dependencies

npm install

Build the Component

npm run build

Produces a WASM file in the out directory ready to be uploaded to Golem!

Using Additional WIT Files (Optional)

If needed you can put additional WIT files from golem-wit (opens in a new tab) to the wit/deps directory in your project.

Then import them to your main interface definition.

For example if you wanted to use a wasi clock you would add the following to your main.wit file:

package golem:component;
 
interface api {
  add: func(value: u64);
  get: func() -> u64;
}
 
world demo {
  // Add the import!
  import wasi:clocks/wall-clock@0.2.0;
  export api;
}

Then you need to add the wasi deps to your wit/deps directory.

We need both folders because clocks depends on the io.

main.wit

package.json

These wasi functions can be imported from your javascript like this:

import { now } from "wasi:clocks/wall-clock@0.2.0"
 
function useNow() {
  let currentTimestamp = now()
  console.log(`The current time is`, currentTimestamp)
}

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