CODE EXAMPLE FOR DART

calculate time difference with now in flutter

var jiffy1 = Jiffy()
      ..add(duration: Duration(days: 1));
jiffy1.yMMMMd; // October 20, 2019

var jiffy2 = Jiffy()
    ..subtract(days: 1);
jiffy2.yMMMMd; // October 18, 2019

//  You can chain methods by using Dart method cascading
var jiffy3 = Jiffy()
     ..add(hours: 3, days: 1)
     ..subtract(minutes: 30, months: 1);
jiffy3.yMMMMEEEEdjm; // Friday, September 20, 2019 9:50 PM

var jiffy4 = Jiffy()
    ..add(duration: Duration(days: 1, hours: 3))
    ..subtract(duration: Duration(minutes: 30));
jiffy4.format("dd/MM/yyy"); // 20/10/2019


// Months and year are added in respect to how many 
// days there are in a months and if is a year is a leap year
Jiffy("2010/1/31", "yyyy-MM-dd"); // This is January 31
Jiffy([2010, 1, 31]).add(months: 1); // This is February 28