Why do I get the wrong date in my browser using javascript date?

Question

I am completely baffled on what is happening with my javascript date. Here is my javascript:

toDate(date) {
  return date instanceof Date ? date : new Date(date)
}

When I pass the string "2016-12-01" to this function, I get this for my date

Wed Nov 30 2016 17:00:00 GMT-0700 (MST)

I am not passing in timezone information, just the string shown above. When I type the same code into my console, I get the same behavior.

Here is another example when I pass in timezone information where the same thing happens.

This is happening Chrome version 55.0.2883.75 (64-bit).

I tested in Firefox 50.0.2 and I am not having this issue.

Any ideas?

Try creating the new Date with a given timezone in ISO format. — Rob, Dec 15 '16 at 20:40
Because you are in GMT -7 timezone. If you want to have 2016-12-01 00:00 then just pass with time `new Date("2016-12-01 00:00")` — Tolgahan Albayrak, Dec 15 '16 at 20:41
I believe if you add the time (00:00:00) to your string, you will get the correct behaviour — nibnut, Dec 15 '16 at 20:42
You shouldn't create a date with a string. Do this: `new Date(2016, 11, 1)` — jwerre, Dec 15 '16 at 20:42
Looks like it's (still) implementation specific: http://stackoverflow.com/a/15110385/278185 — Dave, Dec 15 '16 at 20:49
In the second example, when you type in 'Z', it strictly refers to Zulu time (UTC). When it outputs to the console, it converts it to MST. — , Dec 15 '16 at 21:11

score 1 · Answer 1 · answered Dec 15 '16 at 20:47

Do this instead:

new Date("2016-12-01".split("-"))

Note: parsing of date strings with the Date constructor (and Date.parse, they are equivalent) is strongly discouraged due to browser differences and inconsistencies. Support for RFC 2822 format strings is by convention only. Support for ISO 8601 formats differs in that date-only strings (e.g. "1970-01-01") are treated as UTC, not local.

from MDN

score 0 · Answer 2 · answered Dec 15 '16 at 21:15

If you check out the MDN documentation for the Javascript Date, you will find this warning below the documentation for passing a datestring to the Date constructor:

Note: parsing of date strings with the Date constructor (and Date.parse, they are equivalent) is strongly discouraged due to browser differences and inconsistencies. Support for RFC 2822 format strings is by convention only. Support for ISO 8601 formats differs in that date-only strings (e.g. "1970-01-01") are treated as UTC, not local.

That means that if you pass the date string "2016-12-01", the Date constructor will assume that you mean Midnight December 1st, 2016 UTC, but will then convert the date to your local timezone.

You appear to be on MST (like me!), which is 8 hours behind UTC time. So converting Midnight December 1st, 2016 UTC to MST would be 5PM November 30th, 2016!

Why do I get the wrong date in my browser using javascript date?

2 Answers2