Compile Go to WebAssembly (the browser version)

Posted on December 23, 2019 | 2 minute read

Introduction

I don't think many people realised yet the great possibilities we were given with the advent of WebAssembly.

We are now essentially able to compile almost any (see list) language to WebAssembly. Which means that the range of applications that we can run in a browser, on the client side, has grown exponentially!

For example, I would like to show you below how you can take your Go code, compile it to WebAssembly and run it natively in the browser.

🍖 & 🥔

Let's to this step by step!

  1. Prepare a Go application that you want to convert to WebAssembly. NOte that you can only compile main packages. If your code is not part of a main package then make it so.

Here is what I am going to compile:

package main

import "fmt"

func main() {
	fmt.Println("Hello world!")
}

Classic.

  1. Run the go command to compile your Go code to WASM.
GOOS=js GOARCH=wasm go build -o main.wasm
  1. Copy the glue JS file which will let you execute the compiled WASM in the browser. This is a file located inside your $GOROOT directory.
cp "$(go env GOROOT)/misc/wasm/wasm_exec.js" .
  1. Create a HTML file with the following contents. Note that we are including the wasm.exec.js file that we just copied.
<html>
	<head>
		<meta charset="utf-8"/>
		<script src="wasm_exec.js"></script>
		<script>
			const go = new Go();
			WebAssembly.instantiateStreaming(fetch("main.wasm"), go.importObject).then((result) => {
				go.run(result.instance);
			});
		</script>
	</head>
	<body></body>
</html>
  1. Now you have to spin up a local web server and load the HTML file through it. If you're not sure how to do this, there is a quick way to do it with Go. Just execute the following two commands in the terminal.
go get -u github.com/shurcooL/goexec
goexec 'http.ListenAndServe(`:8080`, http.FileServer(http.Dir(`.`)))'

If everything went well you'll be able to navigate to localhost:8080 and be presented with a blank page. Now open the developer tools and check the console!

Great success!

Automating the process

I have also put together a little script which lets you compile and start the server in one command.

Check out the repository below.

github.com/dorin131/go-to-webassembly

By running compile.sh, all the steps above are going to be executed.

tags:go webassembly compile browser
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