How to get timezone value for new Date(2017,05,31).toISOString()? It always comes as 000Z for any Date when the date is passed to the Date constructor. But for new Date().toISOString(), it gives the the timezone value.
new Date(2017,05,31).toISOString() gives "2017-05-30T18:30:00.000Z"
and new Date().toISOString() gives "2017-06-07T15:29:23.692Z". How to get timezone in UTC format for the past dates?
If you want the time to default to midnight in UTC, you can use Date.UTC(year, month, ...) to first create a timestamp based in UTC.
var utcMay31 = Date.UTC(2017, 4, 31); // note: 4 = May (0 = January)
Then, create the Date from that timestamp.
new Date(utcMay31).toUTCString(); // "Wed, 31 May 2017 00:00:00 GMT"
However, if you're wanting to know the timezone stored in the Date object, it doesn't actually have that. Dates represent an "instant" in time as the total number of milliseconds that have passed since Jan 1, 1970 00:00:00.000 UTC.
new Date().getTime(); // 1496851...
A Date can tell you the user's local offset from UTC in minutes at that instant.
new Date().getTimezoneOffset(); // e.g. 0, -480, 300
Otherwise, the timezone is limited to two choices when creating date strings, and the choice is based on the method used – user's local timezone or UTC.
new Date().toString(); // "now" in user's local time
new Date().toUTCString(); // "now" in UTC time
new Date().toISOString(); // "now" also in UTC time, alternate format
// etc.
You're confused ISO date values do not show the "time zone" instead they show the UTC time. Z stand for Zulu (UTC time).
2017-06-07T15:29:23.692Z
The bold part is not the time zone. It is the milli-seconds, the full time is in UTC. The reason it shows a 000Z in the set Date is because you didnt' set the milli-seconds.
If you want to display the time zone use toUTCString(). However it will display GMT which is UTC/Greenwich Time. To display the local time zone in a the date format you can use date.toLocaleString('en-US',{timeZoneName:'short'}) for example will display the date plus the local US time zone. Or you can use toString() which will display the GMT offset + the long local time zone.
In javascript, parsing, rendering and constructing dates will always assume local. It will convert to a timestamp, the number of milliseconds since 1-1-1970 00:00:00. JSON.stringify will convert to a UTC string, but legacy framworks use local dates. Always beware of this.
var myDate = new Date(); // this is now.
you can get your timezoneoffset (in minutes) with myDate.getTimezoneOffset(), but this will return the same offset for every date (aside from daylight saving time)
You shouldn't do this:
var utcDate = new Date(+d+60000*d.getTimezoneOffset());
// +d convert the date to a timespan.
// getTimezoneOffset() is in minutes
// *60000 makes that in milliseconds, the scale timespans operate upon
Date has a few methods to format dates, but always as local or UTC date. You need to do it manually if you want different time zones.
Note: the Date.UTC(...) function returns a timestamp. You sometimes see shifted dates, so they behave like UTC. But this causes problems later on.
var date = new Date(2000,1,1,12,0,0);
// DO NOT USE (breaks at start of daylight saving time)
// these are date/times that have the UTC-value,
// but Javascript treats them like local dates with this value.
utcDate1 = (+date-60000*d.getTimeZoneOffset()); // minus!!
utcDate2 = new Date(Date.UTC(2000,1,1,12,0,0));
// DO NOT USE (breaks at start of daylight saving time)
BTW Edge, Chrome and Firefox display dates differently in the console: Edge and Firefox always shows local date, Chrome shows UTC. Also, if you change your timezone, Edge will screw up.
