Get attribute names are in the main form of particular entity from systemform entity in dynamics CRM

var serverUrl;
        serverUrl = location.protocol + "//" + location.host;
        function getformfields() {
            debugger;
            var oDataUri = "systemforms?$select=formxml&$filter=name eq 'account'";
            var data = getODataRecords(oDataUri);
            if(data!=null&&data!="")
            {
               //how to get field name from response
            }

        }
        function getODataRecords(ODataUrl) {
            debugger;
            var data;
            var Query = ODataUrl;
            var req = new XMLHttpRequest();

            req.open("GET", serverUrl + "/api/data/v8.0/" + Query, false);
            req.setRequestHeader("Accept", "application/json");
            req.setRequestHeader("Content-Type", "application/json; charset=utf-8");
            req.setRequestHeader("OData-MaxVersion", "4.0");
            req.setRequestHeader("OData-Version", "4.0");
            req.setRequestHeader("Prefer", "odata.include-annotations=OData.Community.Display.V1.FormattedValue");
            req.onreadystatechange = function () {
                if (this.readyState == 4 /* complete */) {
                    req.onreadystatechange = null;
                    if (this.status == 200) {
                        data = JSON.parse(this.response);
                    }
                    else {
                        var error = JSON.parse(this.response).error;
                        alert(error.message);
                    }
                }
            };
            req.send();
            return data;

        }