moment.js diff showing wrong result

Question

I am working on a small script using momentjs, that shows me how many hours and minutes (seperate) I have until a specific hour. But for some reason the result is wrong.

Thats my code so far:

var TimeA = moment('08:00:00', 'HH:mm:ss');
var TimeB = moment('16:00:00', 'HH:mm:ss');

var DiffAB = moment(TimeA.diff(TimeB)).format('HH:mm:ss');

var DiffHours = moment(DiffAB, 'HH:mm:ss').format('H');
var DiffMinutes = moment(DiffAB, 'HH:mm:ss').format('mm');

console.log('TimeA: ' + moment(TimeA).format('HH:mm:ss'));
console.log('TimeB: ' + moment(TimeB).format('HH:mm:ss'));

console.log('Difference A-B: ' + DiffAB);

console.log('Diff Hours: ' + DiffHours);
console.log('Diff Minutes: ' + DiffMinutes);  

And thats the Output:

TimeA: 08:00:00
TimeB: 16:00:00
Difference A-B: 17:00:00
Diff Hours: 17
Diff Minutes: 00  

The difference of A - B should be 8 but its showing 17.

Answer 1

As per momentjs documentation

If the moment is earlier than the moment you are passing to moment.fn.diff, the return value will be negative.

To translate it to your example:

If TimeA is earlier than TimeB passed to moment.diff then the value will be negative

and since it's returned as milliseconds -28800000 is an instruction like: take that amount of miliseconds from midnight, that gives you the different time

so what you should be doing is

var DiffAB = moment(TimeB.diff(TimeA)).utcOffset(0).format('HH:mm:ss');

Diff documentation https://momentjs.com/docs/#/displaying/difference/

Example from doc

An easy way to think of this is by replacing .diff( with a minus operator.

          // a < b
a.diff(b) // a - b < 0
b.diff(a) // b - a > 0