function ajax(method, url,foo) {
    let xhr = new XMLHttpRequest();
    xhr.open(method, url);
    xhr.send();
    xhr.onreadystatechange = function () {
        if (xhr.readyState === 4) {
            if (xhr.status === 200) {
                // console.log(xhr.responseText);
                let data = JSON.parse(xhr.responseText);
                foo(data);
                // return data;
            }
        }
    }

}