How to call method with JS callback

Hi,
is possible to call method with JS callback?
Example:

```
Library.prototype.fetch = function(url,cb,scope) {
var request = new XMLHttpRequest();

request.onreadystatechange = function() {
if (request.readyState==4 && request.status==200) {
cb.call(scope,request.responseText);
}
}
request.open("GET",url,true);
request.send();
}
```

In JS call looks like this:

```
instanceOfLibrary.fetch('_URL_', function(data) {document.getElementById("output").innerHTML = "

Fetched:

"+data+"

If yes, could I ask how to define the callback in interface?

```
@Method("instanceOfLibrary.fetch")
void fetch(String url, ???? , Callback callback);
```

Thank you in advance for any hint!