I'm trying to convert a date (moment) that I store in a db (mongo) and then compare to the current date to get the difference. However, I can't use `diff()` when I retrieve the past date from db and use the current moment. In the db insert, I'm inserting `{startDate:moment(), ...}`. Then, after I retrive the `startDate` date, I try to get diff

```
var now = moment();
console.log(now.diff(startDate))

```

But it throws an [error](https://github.com/moment/moment/issues/1407).

I store the `moment` rather then the js `date` object but I am still getting the error, so I'm not sure how how I'm actually supposed to get the diff of a stored value and compare it to current moment.