I don’t think any of GopherJS developers use or support Windows, so building with GOOS=windows likely doesn’t work. However, you should be able to build with GOOS=linux gopherjs build or GOOS=darwin gopherjs build.

Thank you so much, it works pretty nice. Even features that is not mentioned in the page of compatibilities.

I have one question, I think it's the last one, I don't know if I need to open one new issue. But, It's possible to get data from one <input type="file">? I mean the user "upload" the file, but instead of send it to one server the file is processed locally, using the JS which is compiled from Golang.

Yes, that is absolutely possible.

The <input> element has a files property that you can access. The type is FileList, which contains a list of File objects. You can convert a File to a byte slice and then run any Go code on it.

See https://developer.mozilla.org/en-US/docs/Web/API/HTMLInputElement and https://developer.mozilla.org/en-US/docs/Web/API/FileList.

In the dom wrapper package, the files property is available via the HTMLInputElement.Files method.

I'll take a look in the first alternative, that uses the Javascript. I'm trying with HTMLInputElement.Files but don't have sucess for now, it only show [object File], one of my test was:

js.Global.Get("document").Call("write", `<input class="x" type="file">`)

root := dom.GetWindow().Document()
input := root.QuerySelector(".x")

input.AddEventListener("change", true, func(dom.Event) {
	f := input.(*dom.HTMLInputElement)
	fmt.Println(f.Files()[0].Object.String())
})

In the docs it says "The dom package does not define any methods on File nor does it provide access to the blob or a way to read it.". :\

I found one similar issue, dominikh/go-js-dom#32. I don't know if have a better method, if something change in the GopherJS since this issue. But for now I'm using something based in your code, in the reply. 👍

func blobToBytes(blob *js.Object) []byte {
	var b = make(chan []byte)
	fileReader := js.Global.Get("FileReader").New()
	fileReader.Set("onload", func() {
		b <- js.Global.Get("Uint8Array").New(fileReader.Get("result")).Interface().([]byte)
	})
	fileReader.Call("readAsArrayBuffer", blob)
	return <-b
}

func main() {

	js.Global.Get("document").Call("write", `<input class="x" type="file">`)

	root := dom.GetWindow().Document()
	input := root.QuerySelector(".x")

	input.AddEventListener("change", true, func(dom.Event) {
		go func() {
			result := blobToBytes(input.(*dom.HTMLInputElement).Files()[0].Object)
			fmt.Println(string(result))
		}()
	})
}

If someone have the same problem, but will be nice if the Files have something like .Bytes().

In the docs it says "The dom package does not define any methods on File nor does it provide access to the blob or a way to read it.". :\

Indeed. You need to do it yourself with something like:

// blobToBytes converts a Blob to []byte.
func blobToBytes(blob *js.Object) []byte {
	b := make(chan []byte)
	fileReader := js.Global.Get("FileReader").New()
	fileReader.Set("onload", func() {
		b <- js.Global.Get("Uint8Array").New(fileReader.Get("result")).Interface().([]byte)
	})
	fileReader.Call("readAsArrayBuffer", blob)
	return <-b
}

Edit: You beat me to it. 👍

'GOOS' is not recognized as an internal or external command,
operable program or batch file.

That doesn't seem to work on Windows, but then again, I'm manually inputting it into the commandline + batch file.

@Azareal $env:GOOS="linux"