'use strict';
function getURL(URL) {
    return new Promise(function (resolve, reject) {
        var req = new XMLHttpRequest();
        req.open('GET', URL, true);
        req.onload = function () {
            if (req.status == 200) {
                resolve(req.response);
            } else {
                reject(new Error(req.statusText));
            }
        };
        req.onerror = function () {
            reject(new Error(req.statusText));
        };
        req.send();
    });
}
// 実行例
var URL = "http://httpbin.org/get";
getURL(URL).then(function onFulfilled(value){
    console.log(value);
}).catch(console.error.bind(console));

'use strict';
    function getURL(URL) {
    return new Promise(function (resolve, reject) {
    var req = new XMLHttpRequest();
    req.open('GET', URL, true);
    req.onload = function () {
    if (req.status == 200) {
    resolve(req.response);
    } else {
    reject(new Error(req.statusText));
    }
    };
    req.onerror = function () {
    reject(new Error(req.statusText));
    };
    req.send();
    });
    }
    // 実行例
    var URL = "http://httpbin.org/get";
    getURL(URL).then(function onFulfilled(value){
    console.log(value);
    }).catch(console.error.bind(console));