Quick Tutorial: Write Go, Run WASM!

Before Go 1.11 gets released, which introduces an experimental port to WebAssembly (WASM for short), I'm going to demonstrate how to compile Go source code into WASM and execute in the browser!

Here are the steps:

1. Setup go1.11beta3
2. Compile Go to WASM
3. Use HTML and JavaScript to load WASM
4. Spin up a web server
5. Open the website!

Step 1: Setup go1.11beta3

Although we need Go version 1.11 which is still in beta (due in August!), because Go is open-source we can just download the latest beta instead.

https://github.com/golang/go/releases/tag/go1.11beta3

$ go get golang.org/dl/go1.11beta3
$ go1.11beta3 download
# => Success. You may now run 'go1.11beta3'

Step 2: Compile Go to WASM

We can now write Go! The plan is to print the classic hello, Go/WASM! but in the browser––in the developer console.

// main.go
package main

import "fmt"

func main() {
    fmt.Println("hello, Go/WASM!")
}

To compile our program from Go to WASM, we use the command go build.

Note: We need to tell Go to compile for the web and not the default environment; our computer. So we need to set the environmental variables GOOS=js and GOARCH=wasm to target the web.

$ GOOS=js GOARCH=wasm go1.11beta3 build -o test.wasm main.go

Step 3: Use HTML and JavaScript to load WASM

This step isn't difficult; the Go team has prepared some files for us to experiment with.

# -s == silent mode
# -O == output mode
$ curl -sO https://raw.githubusercontent.com/golang/go/master/misc/wasm/wasm_exec.html
$ curl -sO https://raw.githubusercontent.com/golang/go/master/misc/wasm/wasm_exec.js

Step 4: Spin up a web server

Now we need to spin up a simple web server to serve some static assets. This is just a few lines of code:

// server.go
package main

import (
    "flag"
    "log"
    "net/http"
)

func main() {
    port := flag.String("port", "8000", "port")
    flag.Parse()
    log.Fatal(http.ListenAndServe(":"+*port, http.FileServer(http.Dir("."))))
}

Let's start it! Cheers!

$ go1.11beta3 run server.go

# or to run on a different port:
# $ go1.11beta3 run -port=8080 server.go

Step 5: Open the website!

Open localhost:8000/wasm_exec.html!

Note: A 'Run' button (at the top left) will appear disabled until the compiled WASM is loaded.

Once the 'Run' button is enabled, open the console and press the button!

See hello, Go/WASM!??

Congratulations! 🎉

You've just compiled, loaded, and run a Go program via WASM!

Is that true?

Why don't you confirm that Content-Type is application/wasm in the response header of test.wasm? ;)

Acknowledgements

Thank you ZAYDEK for recommending me to translate my article into English and reviewing this article.

References

• サクッと Go → WebAssembly を試す(Original article in Japanese)
• Go and wasm: generating and executing wasm with Go - Gopher Academy Blog Community Contributed Go Articles and Tutorials