Clone2.19.0+

moment.duration().clone();

Create a clone of a duration. Durations are mutable, just like moment objects,so this lets you get a snapshot, at some point in time.

var d1 = moment.duration();
var d2 = d1.clone();
d1.add(1, 'second');
d1.asMilliseconds() !== d2.asMilliseconds();