Go (golang) WebAssembly (WASM) hello world example

Readme.md

Readme

First, get all files from this gist in a local folder.

Then, copy required html and js files from your go installation:

cp $(go env GOROOT)/misc/wasm/wasm_exec.{html,js} .

Then, run your project:

make

That's it, you are a go-wasm specialist now 😎

main.go

package main

import (
	"syscall/js"
)

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

	add := func (this js.Value, inputs []js.Value) interface{} {
		return js.ValueOf(inputs[0].Int() + inputs[1].Int())
	}

	closeGo := func(this js.Value, inputs []js.Value) interface {} {
		c <- true
		return nil
	}

	setGlobal42 := func (this js.Value, inputs []js.Value) interface {} {
		js.Global().Set("$42", js.ValueOf(42))
		return nil
	}

	js.Global().Set("add", js.FuncOf(add))
	js.Global().Set("closeGo", js.FuncOf(closeGo))
	js.Global().Set("setGlobal42", js.FuncOf(setGlobal42))

	<-c
}

Makefile

serve: compile
	go run server.go

compile: main.go
	GOARCH=wasm GOOS=js go build -o test.wasm main.go

server.go

package main

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

var (
	listen = flag.String("listen", ":8080", "listen address")
	dir    = flag.String("dir", ".", "directory to serve")
)

func main() {
	flag.Parse()
	log.Printf("listening on %q...", *listen)
	log.Fatal(http.ListenAndServe(*listen, http.HandlerFunc(func(resp http.ResponseWriter, req *http.Request) {
		if strings.HasSuffix(req.URL.Path, ".wasm") {
			resp.Header().Set("content-type", "application/wasm")
		}

		http.FileServer(http.Dir(*dir)).ServeHTTP(resp, req)
	})))
}