How to adapt an old JS used for CRM 4.0 to CRM 2015

I'm new at Microsoft Dynamics CRM and I'm working with CRM 2015. I'm working with CRM 2015 and I've been given to fix an error script developed for CRM 4.0.
It looks like an old syntax and I don't know how to adapt it to JS for CRM 2015 or CRM 2016. The script manage the user roles and roles name and I have retrive the data through fetchXML.
I've been told to work with oDATA for crm 2015 or WebApi for CRM 2016.I haven't worked before with webservices and the requirement s are to use fetchXML so i guess i have to work with WebApi and i don't know how to adapt it.

function onChangeValutator()
{
     var idUser = Xrm.Page.getAttribute("erm_valutatorid").getValue()[0].id;

     // Use the Xrm.Page.context.getAuthenticationHeader() method
     // available from the CRM form to generate the Soap header text.
     var authenticationHeader = Xrm.Page.context.getAuthenticationHeader();

     // Define the SOAP XML to access Microsoft Dynamics CRM Web service.
     var xml = "<?xml version=\"1.0\" encoding=\"utf-8\"?>" +"<soap:Envelope xmlns:soap="+"\"schemas.xmlsoap.org/.../envelope\" "+"xmlns:xsi=\"www.w3.org/.../XMLSchema-instance\" "+"xmlns:xsd=\"www.w3.org/.../XMLSchema\">" +
     authenticationHeader+"<soap:Body>" +
     // Specify the RetrieveMultiple message."<RetrieveMultiple xmlns="+"\"schemas.microsoft.com/.../WebServices\">" +
     // Specify that this is a QueryByAttribute query."<query xmlns:q1="+"\"schemas.microsoft.com/.../Query\" "+"xsi:type=\"q1:QueryByAttribute\">" +
     // Query the customeraddress entity."<q1:EntityName>erm_source</q1:EntityName>" +
     // Set the columns you want to return."<q1:ColumnSet xsi:type=\"q1:ColumnSet\">" +"<q1:Attributes>" +"<q1:Attribute>erm_roleid</q1:Attribute>" +"</q1:Attributes>" +"</q1:ColumnSet>" +
     // Specify the attribute that you are querying on."<q1:Attributes>" +"<q1:Attribute>erm_sourceid</q1:Attribute>" +"</q1:Attributes>" +
     // Set the value of the attribute using the customerid
     // value of the case record."<q1:Values>" +"<q1:Value xsi:type=\"xsd:string\">"+
     idUser+"</q1:Value>" +"</q1:Values>" +"</query>" +"</RetrieveMultiple>" +"</soap:Body>" +"</soap:Envelope>";

    var xmlHttpRequest = new ActiveXObject("Msxml2.XMLHTTP");
    xmlHttpRequest.Open("POST", "/mscrmservices/2007/CrmService.asmx", false);
    xmlHttpRequest.setRequestHeader("SOAPAction","schemas.microsoft.com/.../RetrieveMultiple");
    xmlHttpRequest.setRequestHeader("Content-Type", "text/xml; charset=utf-8");
    xmlHttpRequest.setRequestHeader("Content-Length", xml.length);
    xmlHttpRequest.send(xml);
    var doc = xmlHttpRequest.responseXML;
    var source = doc.selectSingleNode("//BusinessEntity");

    var guidSource = source.childNodes[0];

    if (guidSource.text != null)
    {
        // Define the SOAP XML to access Microsoft Dynamics CRM Web service.
         xml = "<?xml version=\"1.0\" encoding=\"utf-8\"?>" +"<soap:Envelope xmlns:soap="+"\"schemas.xmlsoap.org/.../envelope\" "+"xmlns:xsi=\"www.w3.org/.../XMLSchema-instance\" "+"xmlns:xsd=\"www.w3.org/.../XMLSchema\">" +
         authenticationHeader+"<soap:Body>" +
         // Specify the RetrieveMultiple message."<RetrieveMultiple xmlns="+"\"schemas.microsoft.com/.../WebServices\">" +
         // Specify that this is a QueryByAttribute query."<query xmlns:q1="+"\"schemas.microsoft.com/.../Query\" "+"xsi:type=\"q1:QueryByAttribute\">" +
         // Query the customeraddress entity."<q1:EntityName>erm_companyrole</q1:EntityName>" +
         // Set the columns you want to return."<q1:ColumnSet xsi:type=\"q1:ColumnSet\">" +"<q1:Attributes>" +"<q1:Attribute>erm_name</q1:Attribute>" +"</q1:Attributes>" +"</q1:ColumnSet>" +
         // Specify the attribute that you are querying on."<q1:Attributes>" +"<q1:Attribute>erm_companyroleid</q1:Attribute>" +"</q1:Attributes>" +
         // Set the value of the attribute using the customerid
         // value of the case record."<q1:Values>" +"<q1:Value xsi:type=\"xsd:string\">"+
         guidSource.text+"</q1:Value>" +"</q1:Values>" +"</query>" +"</RetrieveMultiple>" +"</soap:Body>" +"</soap:Envelope>";

        xmlHttpRequest = new ActiveXObject("Msxml2.XMLHTTP");
        xmlHttpRequest.Open("POST", "/mscrmservices/2007/CrmService.asmx", false);
        xmlHttpRequest.setRequestHeader("SOAPAction","schemas.microsoft.com/.../RetrieveMultiple");
        xmlHttpRequest.setRequestHeader("Content-Type", "text/xml; charset=utf-8");
        xmlHttpRequest.setRequestHeader("Content-Length", xml.length);
        xmlHttpRequest.send(xml);
        doc = xmlHttpRequest.responseXML;
        var role = doc.selectSingleNode("//BusinessEntity");
        var roleName = role.childNodes[0];

        var lookupItem = new Array();
        lookupItem[0] = new Object();

        lookupItem[0].name = roleName.text;
        lookupItem[0].entityType = "erm_companyrole";
        lookupItem[0].id = guidRSource.text;

        Xrm.Page.getAttribute("erm_valutatorroleid").setValue(lookupItem);

    }
}