         if (xhr.readyState == 4 && xhr.status == 200) {
                let obj = JSON.parse(xhr.response);
                let headers = xhr.getAllResponseHeaders();
                let arr = headers.trim().split(/[\r\n]+/);
                let headerMap = {};
                arr.forEach(function (line) {
                    let parts = line.split(': ');
                    let header = parts.shift();
                    let value = parts.join(': ');
                    headerMap[header] = value;
        