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npm install --save-dev @fiedka/golang-wasm-async-loader

This is a loader for webpack that is used for generating WebAssembly (aka WASM) bundles from Go.

The JavaScript bridge that is then generated for webpack will expose the WebAssembly functions as a Promise for interacting with.

webpack config

module.exports = {
    ...
    module: {
        rules: [
            {
                test: /\.go/,
                use: ['golang-wasm-async-loader']
            }
        ]
    },
    node: {
        fs: 'empty'
    }
};

Using in your code

You import your Go code just like any other JavaScript module you might be working with. The webpack loader will export a default export that has the functions you registered in Go on it. Unfortunately it currently doesn't provide autocomplete of those function names as they are runtime defined.

import wasm from './main.go'

async function init() {
  const result = await wasm.add(1, 2);
  console.log(result);

  const someValue = await wasm.someValue();
  console.log(someValue);
}

Here's the main.go file:

package main

import (
  "strconv"
  "syscall/js"
  "github.com/fiedka/webpack-golang-wasm-async-loader/gobridge"
)

func add(i []js.Value) (interface{},error) {
	ret := 0

	for _, item := range i {
		val, _ := strconv.Atoi(item.String())
		ret += val
	}

	return ret, nil
}

func main() {
	c := make(chan struct{}, 0)

	gobridge.RegisterCallback("add", add)
	gobridge.RegisterValue("someValue", "Hello World")

	<-c
}

How does it work?

As part of this repository a Go package has been created to improve the interop between the Go WASM runtime and work with the async pattern the loader defines.

To do this a function is exported from the package called RegisterCallback which takes two arguments:

• A string representing the name to register it as in JavaScript (and what you'll call it using)
• The func to register as a callback
  • The func must has a signature of (args js.Value) (interface{}, error) so you can raise an error if you need

If you want to register a static value that's been created from Go to be available in JavaScript you can do that with RegisterValue, which takes a name and a value. Values are converted to functions that return a Promise so they can be treated asynchronously like function invocations.

In JavaScript a global object is registered as __gobridge__ which the registrations happen against.

Examples

Examples are provided for a CLI using NodeJS and for web using either React or Svelte. These are in the examples directory, each with its own development and build environment.

To make an example stand-alone, copy of the corresponding example to a new directory (outside the plugin directory) and then modify the example's webpack.config.js so that the .go loader refers to this plugin. Then add it to the example's dependencies as follows.

For use with Go 1.13, use happybeing's v1.0.6 of the plugin:

npm add --save-dev [email protected]`

For use with Go 1.15, use happybeing's v1.1.0 of the plugin:

npm add --save-dev [email protected]`

For use with Go 1.16, use happybeing's v3.0.2 of the plugin:

npm add --save-dev @fiedka/[email protected]`

Environment

To build your project (and the examples) you will need the GOROOT environment variable set. So for example if using the bash shell:

node example:

GOROOT=`go env GOROOT` npm run predemo
npm run demo

web example (with hot reloading):

GOROOT=`go env GOROOT` npm run build
GOROOT=`go env GOROOT` npm run start

Licence

MIT

Credit

Aaron Powell (updates up to Go 1.15 by Mark Hughes)