Is British Summer time BST

isBritishSummerTimeInEffect.ts

export function isBritishSummerInEffect(date: Date) {
  const possibleBstHour = parseInt(
    date
      .toLocaleTimeString("en-GB", { timeZone: "Europe/London" })
      .split(":")[0],
  );
  const utcHour = date.getUTCHours();

  return possibleBstHour !== utcHour;
}

export function isCurrentlyBritishSummerTime() {
  return isBritishSummerInEffect(new Date())
}

I think this is incorrect, shouldn't line 7 be date.getUTCHours()? Instead of now.getUTCHours()?

Nice spot! Where I initially used this just checked if BST was currently in effect. I added the date argument as a quick upgrade, but forgot to update that line. Cheers 👍