code: function toSeconds() {
        var seconds = this.seconds + 60 * this.minutes + 3600 * this.hours +
                      86400 * this.days + 7 * 86400 * this.weeks;
        return (this.isNegative ? -seconds : seconds);
      }
docs: The duration value expressed as a number of seconds.
  
  @return {Number}             The duration value in seconds