moment.js - isBetween() method doesn't work consistently

Question

I have a moment.js code that works well:

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

But when I start refactoring to make it more readable it fails to work:

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

Answer 1

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

You are passing a reference which you have edited by adding 30 days.