js Date changes on october 10th (BST)

Question

Why does JS Date object change toUTCString on October 10th?

new Date('2017-10-9').toUTCString()
"Sun, 08 Oct 2017 23:00:00 GMT"



new Date('2017-10-10').toUTCString()
"Tue, 10 Oct 2017 00:00:00 GMT"

I am writing these in the UK. BST ends on October 29th. What is going on?!

Since you're not using a proper date format, parsing using the Date constructor is implementation-dependent. — Heretic Monkey, Jun 05 '17 at 16:17

Michał Perłakowski · Answer 1 · 2017-06-05T16:19:58.733

3

In the first example the date is parsed as local date, and in the second as UTC date. To parse the first date as UTC too, add a 0 before 9.

console.log(new Date('2017-10-09').toUTCString()); // Mon, 09 Oct 2017 00:00:00 GMT

Inconsistencies in date parsing like that are why you should always pass a date in ISO-8601 format to the Date constructor. You can also use a library like Moment.js.

edited Jun 05 '17 at 16:19

answered Jun 05 '17 at 16:17

Michał Perłakowski

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I think I might cry – dafyddPrys Jun 05 '17 at 16:19
@dafyddPrys https://cdn.meme.am/cache/instances/folder662/65251662.jpg – Michał Perłakowski Jun 05 '17 at 16:20
"*Inconsistencies in date parsing*" are why you shouldn't use the built-in parser at all! ;-) – RobG Jun 05 '17 at 20:52

js Date changes on october 10th (BST)

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