Ajax.js

'use strict';

let Ajax = {};

Ajax.xhr = () => {
    let xhr, versions;

    if(typeof XMLHttpRequest !== undefined) {
        xhr = new XMLHttpRequest();
    } else {
        versions = [
          'MSXML2.XmlHttp.5.0',
          'MSXML2.XmlHttp.4.0',
          'MSXML2.XmlHttp.3.0',
          'MSXML2.XmlHttp.2.0',
          'Microsoft.XmlHttp'
        ];

        for(let i = 0; i < versions.length; i++) {
            try {
                xhr = new ActiveXObject(versions[i]);
                break;
            } catch (e) {
                throw e;
            }
        }
    }
    return xhr;
};

Ajax.send = (url, method, data, sync) => {
    let promise = new Promise((resolve, reject) => {
        let xhr = Ajax.xhr();
        // withCredentials
        xhr.withCredentials = true;
        xhr.open(method, url, sync);
        xhr.onreadystatechange = () => {
            if (xhr.readyState === 4) {
                resolve(xhr.responseText);
            } else {
                reject(new Error(xhr.statusText));
            }
        }

        if (method === 'POST') {
            xhr.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
        }

        xhr.send(data);
    });
    return promise;
};

Ajax.get = (url, data, callback, sync) => {
    let query = [];
    for (let key in data) {
        query.push(encodeURIComponent(key) + '=' + encodeURIComponent(data[key]))
    }
    url += '?' + query.join('&');
    Ajax.send(url, 'GET', null, sync).then((res) => {
        callback && callback(res);
    });
};

Ajax.post = (url, data, callback, sync) => {
    let query = [];
    for (let key in data) {
        query.push(encodeURIComponent(key) + '=' + encodeURIComponent(data[key]))
    }
    Ajax.send(url, 'POST', query.join('&'), sync).then((res) => {
        callback && callback(res);
    })
};