Date minus date is not giving desired answer - IONIC 2 - ionic-framework

Question

When I try to subtract
Wed Dec 06 2017 15:58:59 GMT+0530 (India Standard Time) minus Tue Nov 28 2017 00:00:00 GMT+0530 (India Standard Time) , the answer which is coming is -22
But the answer should be 6
What is going wrong and where, below is my page.ts code:
this.tt = new Date();
this.tt1 = this.datePipe.transform(this.tt,'dd/mm/yyyy');
console.log(this.ent[0],"server DATE");
// in console we see this - 28-NOV-17 server DATE
var firstDate= new Date(this.ent[0]); //Jan 01 2017 00:00:00
var secondDate = new Date();//Jan 04 2017 00:00:00
console.log(firstDate);
// answer in console - Tue Nov 28 2017 00:00:00 GMT+0530 (India Standard Time)
console.log(secondDate);
//answer in console - Wed Dec 06 2017 15:58:59 GMT+0530 (India Standard Time)
console.log(secondDate.getDate() - firstDate.getDate() );
//answer in console - -22

Answer 1

Date.getDate() gives the "dd" of the date (in your case 6 and 28 which explains the result being -22).
I'm a bit confused with the expected result being 6. So maybe my answer won't fit you. What I would do however is convert the date in time, do the substraction and convert it back to number of days.
So
Math.Floor((secondDate.getTime() - firstDate.getTime()) / 86400000);
(86400000 being 1000 (milliseconds) * 3600 (seconds in an hour) * 24 (number of hours in a day)

Answer 2

you can convert both dates to timestamp and subtract the timestamp you will get the result days in millis now convert it to days
getTimestamp(dateParam:string):string{
var date = new Date(dateParam); // some mock date
var milliseconds = date.getTime();
return milliseconds.toString();
}
var one_day=1000*60*60*24;
console.log(Math.ceil(getTimestamp(secondDate) - getTimestamp(firstDate))/(one_day) );