CRM Output Parameters in Custom Workflow Activity in JavaScript

function ExecuteActionArchiveDocument(IDs, DocumentDescription, entityId, entityName, requestName) {
    // Creating the request XML for calling the Action
    var requestXML = ""
    requestXML += "<s:Envelope xmlns:s=\"schemas.xmlsoap.org/.../envelope\">";
    requestXML += "  <s:Body>";
    requestXML += "    <Execute xmlns=\"schemas.microsoft.com/.../Services\" xmlns:i=\"www.w3.org/.../XMLSchema-instance\">";
    requestXML += "      <request xmlns:a=\"schemas.microsoft.com/.../Contracts\">";
    requestXML += "        <a:Parameters xmlns:b=\"schemas.datacontract.org/.../System.Collections.Generic\">";
    requestXML += "          <a:KeyValuePairOfstringanyType>";
    requestXML += "            <b:key>Target</b:key>";
    requestXML += "            <b:value i:type=\"a:EntityReference\">";
    requestXML += "              <a:Id>" + entityId + "</a:Id>";
    requestXML += "              <a:LogicalName>" + entityName + "</a:LogicalName>";
    requestXML += "              <a:Name i:nil=\"true\" />";
    requestXML += "            </b:value>";
    requestXML += "          </a:KeyValuePairOfstringanyType>";
    requestXML += "          <a:KeyValuePairOfstringanyType>";
    requestXML += "            <b:key>SelectedIDs</b:key>";
    requestXML += "            <b:value i:type=\"c:string\" xmlns:c=\"www.w3.org/.../XMLSchema\">" + documentIDs + "</b:value>";
    requestXML += "            <b:key>DocumentDescription</b:key>";
    requestXML += "            <b:value i:type=\"c:string\" xmlns:c=\"www.w3.org/.../XMLSchema\">" + DocumentDescription + "</b:value>";
    requestXML += "          </a:KeyValuePairOfstringanyType>";
    requestXML += "        </a:Parameters>";
    requestXML += "        <a:RequestId i:nil=\"true\" />";
    requestXML += "        <a:RequestName>" + requestName + "</a:RequestName>";
    requestXML += "      </request>";
    requestXML += "    </Execute>";
    requestXML += "  </s:Body>";
    requestXML += "</s:Envelope>";
    var req = new XMLHttpRequest();
    req.open("POST", GetClientUrl(), false)
    req.setRequestHeader("Accept", "application/xml, text/xml, */*");
    req.setRequestHeader("Content-Type", "text/xml; charset=utf-8");
    req.setRequestHeader("SOAPAction", "schemas.microsoft.com/.../Execute");
    req.onreadystatechange = function () { assignResponse(req); };
    req.send(requestXML);
}