The following code when executed using w3schools’ interactive js environment ( here ): var

Question

Asked: May 18, 20262026-05-18T10:37:32+00:00 2026-05-18T10:37:32+00:00

The following code when executed using w3schools’ interactive js environment (here):

var d1=new Date(1306796400000);
document.write("Original form: " + d1);

displays the following message:

Original form: Tue May 31 2011 00:00:00 GMT+0100 (GMT Daylight Time)

But this:

var d1=new Date(1231977600000);
document.write("Original form: " + d1);

displays this message:

Original form: Thu Jan 15 2009 00:00:00 GMT+0000 (GMT Standard Time)

I thought that the millisecond value was just milliseconds since 01/01/1970 in UTC.
But it looks like it contains a flag for time zone.

Can anyone say what the millisecond value format is?

Thanks in advance.

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Editorial Team · Answer 1 · 2026-05-18T10:37:33+00:00

Editorial Team

There is no special flag. It’s just Daylight Savings in effect.

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