Javascript moment.js-isBetween（）方法不'；我不能始终如一地工作

我有一个moment.js代码运行良好：

var startDate = '2015-05-06T19:00:00+0300';
moment(startDate).isBetween(moment(), moment().add(30, 'days'));
// returns true, that's great!

但当我开始重构以使其更具可读性时，它无法工作：

var today = moment();
var startDate = '2015-05-06T19:00:00+0300'; 
moment(startDate).isBetween(today, today.add(30, 'days'));
// returns false.. but why?

---

您正在通过添加30天的方式传递一个已编辑的引用。

它也会咬到我。谢谢

var today = moment();
var startDate = '2015-05-06T19:00:00+0300'; 
moment(startDate).isBetween(today, moment(today).add(30, 'days'));