let call_backend = function(e) {
    console.log("Call backend");
    type = event.target.getAttribute('name');
    console.log(type);

    var url = document.forms["link"]["url-field"].value;
    var run = document.forms["link"]["run-field"].value;
    var link = document.forms["link"]["link-field"].value;

    xmlhttp = new XMLHttpRequest();
    xmlhttp.onreadystatechange = function() {
        if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
            document.getElementById("result").innerHTML = xmlhttp.responseText;
        };
    };
    xmlhttp.open("POST", url + "/link/" (type==="start" ? "start" : "handoff") + "/" + run + "/" + link, true);
    xmlhttp.send();
}