你绝对不了解的promise

        'use strict';

        // 清除log:
        var logging = document.getElementById('test-promise-log');
        while (logging.children.length > 1) {
            logging.removeChild(logging.children[logging.children.length - 1]);
        }

        // 输出log到页面:
        function log(s) {
            var p = document.createElement('p');
            p.innerHTML = s;
            logging.appendChild(p);
        }
        new Promise(function (resolve, reject) {
            log('start new Promise...');
            var timeOut = Math.random() * 2;
            log('set timeout to: ' + timeOut + ' seconds.');
            setTimeout(function () {
                if (timeOut < 1) {
                    log('call resolve()...');
                    resolve('200 OK');
                }
                else {
                    log('call reject()...');
                    reject('timeout in ' + timeOut + ' seconds.');
                }
            }, timeOut * 1000);
        }).then(function (r) {
            log('Done: ' + r);
        }).catch(function (reason) {
            log('Failed: ' + reason);
        });