ES6-Promise
JavaScript 异步编程:https://www.runoob.com/js/js-async.html
JavaScript Promise 对象:https://www.runoob.com/w3cnote/javascript-promise-object.html , https://www.runoob.com/js/js-promise.html
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise