TIL post around timezones in JS

src/blog/posts/2024/2/why-is-date.parse-weird-in-gmt.md

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+---
+title: "TIL: Why Date.parse gives unexpected results for GMT"
+tags:
+    - Javascript
+    - TIL
+---
+
+TL;DR: Timezones are weird
+
+Someone posted about this in a Discord server I'm on: Javascript's Date object has a parse function, [Date.parse](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/parse) that takes a string can converts it to a timestamp. If you give it a non-standard string, in this case `Jan 1, 1970`, it should still parse it.
+
+The problem is though, that even though we're in GMT, and `GMT == UTC`, `Date.parse("Jan 1, 1970")` results in a timestamp of `-3600000`, or Dec 31, 1969 23:00:00. If you explicitly add the GMT timezone, it's fine.
+
+It turns out that if you omit the timezone, `Date.parse` will use your system timezone - now in my case that's GMT _today_[^1], but if I were to go back to 1970 I'd actually find that I'd be in BST. This is because the government [experimented with scrapping daylight savings](https://www.rmg.co.uk/stories/topics/uk-time-british-summer-time-bst-daylight-saving). So, when you parse that specific date, your timezone is actually `UTC+1`.
+
+[^1]: Obviously this only breaks in the UK
+
+