MomentJS - utcOffset() not applying offset?

user_3068500 0
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I have the following code:

const thresholdDate = "2020-02-12";
const value = "2020-02-12T01:00+02:00";

const valueUtcOffset = moment.parseZone(value).utcOffset();

const thresholdDateWithOffset = moment.utc(thresholdDate).utcOffset(valueUtcOffset);

console.log(moment(value).isBefore(thresholdDateWithOffset))


const thresholdDate = "2020-02-12";
const value = "2020-02-12T01:00+02:00";

const valueUtcOffset = moment.parseZone(value).utcOffset();

const thresholdDateWithOffset = moment.utc(thresholdDate).utcOffset(valueUtcOffset);

console.log(moment(value).isBefore(thresholdDateWithOffset))
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.17.1/moment.min.js"></script>

The result of valueUtcOffset is 120.

However, the console.log() returns true and i don't understand why.

value with the UTC offset is 2020-02-11 11PM, whereas thresholdDateWithOffset should be 2020-02-11 10PM.

So how come it says that value is before thresholdDateWithOffset?

momentjs javascript
2 Answers

Your assumption here is wrong:

value with the UTC offset is 2020-02-11 11PM, whereas thresholdDateWithOffset should be 2020-02-11 10PM.

thresholdDateWithOffset will actually be midnight utc, while value is 11 pm the day before. When you put moment.utc("2020-02-12") you are creating midnight in utc. When you apply the offset moment.utc("2020-02-12").utcOffset(120) it will still be midnight in utc, but represented as "2020-02-12T02:00+02:00". You're just changing the offset the time appears as, you're not really changing the time. The real time used when comparing times remains the same.

user_79334780

The behavior of your snippet is correct. You take timezone which is UTC+2 ( + 120 )

you ask moment to give you a date const thresholdDateWithOffset = moment.utc(thresholdDate).utcOffset(valueUtcOffset); on that timezone.

const thresholdDateWithOffset = moment.utc(thresholdDate).utcOffset(valueUtcOffset); //"2020-02-12T02:00+02:00"

then you check if "2020-02-12T01:00+02:00" is before "2020-02-12T02:00+02:00" and it answered true which is true

moment.utc("2020-02-12") => 2020-02-12T00:00+00:00
moment.utc("2020-02-12").utcOffset(120) => 2020-02-12T02:00+02:00



moment.utc("2020-02-12T00:00+02:00") => 2020-02-11T10:00+00:00
moment.utc("2020-02-12T00:00+02:00").utcOffset(120) => 2020-02-12T00:00+02:00
user_107024480
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