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Compiling to WebAssembly with Go

First, create a new directory and navigate into it. Then, create a new file called main.go and add the following code to it. Run go mod init wasm to create a new module.

The code:

package main


import (
  "syscall/js"
)


func main() {
  js.Global().Set("sayHello", js.FuncOf(sayHello))
  select {}
}


func sayHello(this js.Value, args []js.Value) interface{} {
  return "Hello, " + args[0].String() + "!"
}

Next, you need to copy the wasm_exec.js file from the Go installation directory to your project directory. You can find the file in the misc/wasm directory of the Go installation.

Terminal window
cp "$(go env GOROOT)/misc/wasm/wasm_exec.js" .

Finally, set up your index.html file to load the WebAssembly module.

<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>

Now, you can run the following command to compile the Go code to WebAssembly.

Terminal window
GOOS=js GOARCH=wasm go build -o main.wasm

This will create a main.wasm file in your project directory.

Run a local server to serve the index.html file. e.g. use “serve”:

Terminal window
npm install -g serve
serve .

Last but not least, you can execute the defined function in the main.go file from the browser console.

sayHello("WebAssembly")

And you should see the following output in your browser console:

Hello, WebAssembly!