Return new Promise((resolve) => {

Question

Return new Promise((resolve) => {

let xhr = new XMLHttpRequest();
xhr.open(options.method || 'GET', url, false);
xhr.onreadystatechange = function () {
if (xhr.status !== 200)
console.log('Ошибка сервера: ' + this.status);
};
xhr.setRequestHeader('Content-Type', 'application/json;charset=UTF-8');
xhr.send(JSON.stringify(options.data));

xhr.onload = function () {
resolve('response' in xhr ? xhr.response : xhr.responseText);
}
});