var serverSelection;
var nickname;

window.onload = function() {
    document.getElementById("formID").onsubmit = onFormSubmit;
    nickname = document.getElementById("inputVonNicknameId");
}


function onFormSubmit(e) {

    e.preventDefault();

    var fdata = new FormData();
    fdata.append("nickname", nickname.value);

    open({
        type: "POST",
        url: "test.php",
        data: fdata,
        success: function(data) {
            code kommt hier von data
        },
        error: function() {
            console.log("Something went wrong");
        }
    });

    return false;

}