code.js

function addContact()
{
    var newFirst = document.getElementById("firstName").value;
    var newLast = document.getElementById("lastName").value;
    var newNumber = document.getElementById("colorText").value;

    var jsonPayload = '{"firstName" : "' + newFirst + '", "lastName" : ' + newLast + '", "phoneNumber" : ' + newNumber + '}';

    var url = urlBase + '/AddContact.' + extension;

    var xhr = new XMLHttpRequest();
    xhr.open("POST", url, true);
    xhr.setRequestHeader("Content-type", "application/json; charset=UTF-8");
    try
    {
        xhr.send(jsonPayload);
    }
    catch(err)
    {
        document.getElementById("colorAddResult").innerHTML = err.message;
    }

}