How do you convert a JavaScript date to UTC?

Question

Suppose a user of your website enters a date range.

2009-1-1 to 2009-1-3

You need to send this date to a server for some processing, but th

Answer 1

Browsers may differ, and you should also remember to not trust any info generated by the client, that being said, the below statement works for me (Google Chrome v24 on Mac OS X 10.8.2)

var utcDate = new Date(new Date().getTime());

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edit: "How is this different than just new Date()?" see here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date

• If no arguments are provided, the constructor creates a JavaScript Date object for the current date and time according to system settings.
• Note: Where Date is called as a constructor with more than one argument, the specifed arguments represent local time. If UTC is desired, use new Date(Date.UTC(...)) with the same arguments. (note: Date.UTC() returns the number of millisecond since 1970-01-01 00:00:00 UTC)

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Adding the 60000 * Date.getTimezoneOffset() as previous answers have stated is incorrect. First, you must think of all Dates/Times as already being UTC with a timezone modifier for display purposes.

Again, browsers may differ, however, Date.getTime() returns the number of milliseconds since 1970-01-01 UTC/GMT. If you create a new Date using this number as I do above, it will be UTC/GMT. However, if you display it by calling .toString() it will appear to be in your local timezone because .toString() uses your local timezone, not the timezone of the Date object it is called on.

I have also found that if you call .getTimezoneOffset() on a date, it will return your local timezone, not the timezone of the date object you called it on (I can't verify this to be standard however).

In my browser, adding 60000 * Date.getTimezoneOffset() creates a DateTime that is not UTC. However when displayed within my browser (ex: .toString() ), it displays a DateTime in my local timezone that would be correct UTC time if timezone info is ignored.