Why converting new.Date() .toISOString() changes the time?

Question

I'm inserting a date in a database in two different format.

this is inserting as Datetime

    var mydate;
    mydate = new Date();
    document.getElementById('clockinhour').value = mydate.toISOString().slice(0, 19).replace('T', ' ');

Output A

2017-06-21 20:14:31 

this is inserting as varchar :

document.getElementById('clocked_in_time').value = Date();

Output B

Wed Jun 21 2017 16:14:31 GMT-0400 (Eastern Standard Time)

Output B is the correct time but I need to display output A. What causes the time to change when converted toISOString? How can I fix this?

Answer 1

ISO time is time zone free. You'll notice with b you have time zone GMT-04:00 if you add those four hours to the 16 hours in the Date, you get 20

Answer 2

In your this is inserting as Datetime block your slice are stripping of the timezone part (the Z at the end of toISOString output):

document.getElementById('clockinhour').value = mydate.toISOString().slice(0, 19).replace('T', ' ');

As pointed out by @RobG in the comments section, toISOString should always return the date in UTC (Z or +00:00).

RTFM: "The time zone [offset] is always UTC, denoted by the suffix Z",

The time "changes" because it is converted to UTC when you calls toISOString.

If you want to get ISO date in your timezone, you should take a look in these two questions: How to ISO 8601 format a Date with Timezone Offset in JavaScript? and How to format a JavaScript date