create javascript Date object from string YYYY-MM-DD in local timezone

Question

I have built an application that is using pure javascript Date objects and date-fns for formatting and manipulating the objects.

The application functions perfectly in GMT where I developed it however I'm now on the West Coast of The States and I've discovered that many of my date objects are thrown out because of the timezone difference.

I am creating date objects from strings, either just YYYY-MM-DD or YYYY-MM-DD HH:mm, for example new Date('2018-01-19') or new Date('2018-01-19 08:00').

The issue is that when I create a date from a string of the format YYYY-MM-DD it creates the object disregarding the local timezone.

const date1 = new Date('2018-01-19');
const date2 = new Date('2018-01-19 00:00');

const dateString1 = format(date1, 'YYYY-MM-DD');     // gives '2018-01-18'
const dateString2 = format(date2, 'YYYY-MM-DD');     // gives '2018-01-19'

The behaviour is not consistent depending on whether you pass a time or not. If you pass a time then the date object is fixed to the local timezone, but if you don't then it is fixed to UTC. What I would like is that if I pass a datestring without the time (just year, month and day) that it would also create a date object assuming that it would be the start of the day in the local timezone.

Why is this? And do I just have to set the time as 00:00 each time I create a Date object?

Does this answer your question? Parse YYYY-MM-DD dates using the local timezone — Oswaldo
– Oswaldo, Commented Oct 7, 2020 at 18:11

Herohtar · Accepted Answer · 2018-01-20 02:45:28Z

1

"Why is this?"

From the documentation: "Support for ISO 8601 formats differs in that date-only strings (e.g. "1970-01-01") are treated as UTC, not local."

Parsing dates from strings isn't really advised; the recommendation is to do it manually by splitting the string and using the individual components as parameters. Or use a date library.

answered Jan 20, 2018 at 2:45

Herohtar

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oldo.nicho Over a year ago

Sweet. Thanks for that. I wonder why they decided on this? It's not consistent behaviour... Anyway, I have created a little helper function that I pass the date string to when creating date objects and it simply tacks on a 00:00 on the end of the string if required: return new Date(dateString.length > 10 ? dateString : ${dateString} 00:00). Seems to be doing the trick :-)

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