interval.js
function () {
            if (this._duration) {
                return this._duration;
            }
            if (this._start && this._end) {
                return moment.duration(this._end - this._start);
            }
            else {
                return moment.duration(0);
            }
        }
function () {
            if (this._duration) {
                return this._duration;
            }
            if (this._start && this._end) {
                return moment.duration(this._end - this._start);
            }
            else {
                return moment.duration(0);
            }
        }
function ( ) { if ( this . _duration ) { return this . _duration ; } if ( this . _start && this . _end ) { return moment . duration ( this . _end - this . _start ) ; } else { return moment . duration ( 0 ) ; } }
The duration of a single repition of the interval
The duration of a single repition of the interval