Weird behaviour from JS Date() object

Question

I want to represent the first of a given month, say 1st of Septemeber 2020. When I do this in my console, I get the below output:

$ node
> new Date(2020, 8, 1)
2020-08-31T23:00:00.000Z

How come it returns 2020-08-31 instead of 2020-08-01? What am I doing wrong?

the representation is in UTC , while the date constructor uses the timezone of your browser, which is `+01:00` — Derlin, Aug 11 '20 at 15:47
Months are zero-based in JavaScript. 0 = January, 8 = September. — Heretic Monkey, Aug 11 '20 at 15:47
See also [Javascript Date.UTC() function is off by a month?](https://stackoverflow.com/q/1507619/215552) — Heretic Monkey, Aug 11 '20 at 15:49
@AnuragSrivastava Why do you say that? They entered `new Date(2020, 8, 1)` and expected `2020-08-01`... — Heretic Monkey, Aug 11 '20 at 15:52
@HereticMonkey Oh, I think I speed-read the question missing the last line. Apologies — Anurag Srivastava, Aug 11 '20 at 15:53
The issue wasn't with zero indexed months in the Date object, but that I assumed that the output would have zero indexed months too @HereticMonkey — gullerg, Aug 11 '20 at 15:56

Derlin · Accepted Answer · 2020-08-11T15:56:33.343

0

The output

2020-08-31T23:00:00.000Z

is ISO format, and the Z shows the date is in UTC. When you call the Date constructor, it is using your browser timezone by default, which I can assume is +01:00. Moreover, month indice in the constructor is zero-based.

If what you want is the beginning of the month in UTC, you can do:

d = new Date(Date.UTC(2020, 8, 01))
d.toISOString()
"2020-09-01T00:00:00.000Z"

edited Aug 11 '20 at 15:56

answered Aug 11 '20 at 15:47

Derlin

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Okay thanks, I get what you're saying - I was reading the output date with zero indexed months in mind although it shouldn't be read like that. And yeah, the timezone was confusing me slightly too. Thanks for your help – gullerg Aug 11 '20 at 15:54
1

This answer is the same as in the identified duplicate and should not be marked as the answer... – Heretic Monkey Aug 11 '20 at 15:59

score 0 · Answer 2 · answered Aug 11 '20 at 15:50

0

try

new Date(2020, 7, 1)

because date object is count from 0-11 no 1-12

answered Aug 11 '20 at 15:50

TalOrlanczyk

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Weird behaviour from JS Date() object

2 Answers2