Asynchronous

If you want to retrieve data from a web page then the custom function needs to be asynchronous.
When calling external web services you must do the following:
Return a JavaScript Promise to Excel
Make the http request to call the external service
Resolve the promise using the setResult callback to send the values to Excel.

function method_from_server(arg1) { 
        return Excel.Promise( function (setResult, setError) { 
                getSomethingFromServer_Method(arg1, function(data) { setResult(data.returnedobject); }); 
        }); 
} 

function method_from_server(arg1){ 
    return new OfficeExtension.Promise(function(setResult, setError){ 
        getSomethingFromServer_Method(arg1, function(data) { 
            setResult(data.returnedobject); 
        }); 
    }); 
}