Javascript Date and java.util.Date constructor argument

Question

Yes, another question about Date in Java and Javascript.

The timezone is GMT+4 (Moscow) both in Java and Browser (Chrome).

<script language="javascript">
  var d = new Date(170798400000);
  document.write(d);
</script>

Gives: Sun Jun 01 1975 00:00:00 GMT+0400 (Russian Standard Time)

public class Test {
    public static void main(String[] args) {
        java.util.Date d = new java.util.Date(170798400000L); // the same epoch value!
        System.out.println(d);
    }
}

Gives: Sat May 31 23:00:00 MSK 1975

If I change the epoch value to something like 2011-2012 year (after daylight saving was canceled in Russia) the output is OK. Timezone updater tool ran OK.

Is this a bug or documented feature? Is there any way to handle this except formatting and re-parsing like YYYY-MM-dd HH:mm:SS or so?

from javadoc:

Date(long date)

Allocates a Date object and initializes it to represent the specified number of milliseconds since the standard base time known as "the epoch", namely January 1, 1970, 00:00:00 GMT.

from javascript reference:

new Date(milliseconds)

milliseconds - Integer value representing the number of milliseconds since 1 January 1970 00:00:00 UTC (Unix Epoch).

Answer 1

Is this a bug or documented feature?

This is not a bug with Javascript. At least, I see no way I could claim that.

The browser's Javascript engine is returning the time converted to "GMT+4". What you are wanting, apparently, is MSK which is different from GMT+4 (as noted in your comment). Javascript not knowing about MSK doesn't count as a bug, but a lack of a feature. Perhaps js is "wrong" for not having that detailed knowledge of timezones, but it's not a bug.

Is there any way to handle this except formatting and re-parsing like YYYY-MM-dd HH:mm:SS or so?

Keeping track of all the arbitrary details of timezones requires a lot of work. I know of no such codebase which has all that work available for javascript. Therefore, I believe that, yes, you would have to manually code that conversion yourself if you want to use true MSK.

Answer 2

String representation of time (like "Sun Jun 01 1975 00:00:00 GMT+0400") are used for human. Time value (milliseconds since 1 January, 1970 UTC) are used for storage and calculation.

There is no bug there. In JavaScript, according to the specification, the contente of string representation is implementation-dependant. In Java, according to the documentation, the daylight saving time may be reflected.

From JavaScript specification:

15.9.5.2 Date.prototype.toString ( )

This function returns a String value. The contents of the String are implementation->dependent, but are intended to represent the Date in the current time zone in a convenient, human-readable form.

From Java documentation:

java.util.Date, public String toString()

Converts this Date object to a String of the form: dow mon dd hh:mm:ss zzz yyyy

where:
...
zzz is the time zone (and may reflect daylight saving time).`