Prevent toIsoString to change day

Question

When I do this:

new Date('4/7/2018').toISOString();

I get: "2018-04-06T22:00:00.000Z"

How can I get an ISO string but without the date changing from 7 to 6? I basically want the same date, month and year.

score 2 · Answer 1 · answered Apr 30 '18 at 13:01

2

Use 2018Z in your year field:

var res = new Date('4/7/2018Z').toISOString();
console.log(res);

answered Apr 30 '18 at 13:01

Ankit Agarwal

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Can you explain why is this happening and what is that Z? – Hommer Smith Apr 30 '18 at 13:10
Specifying `Z` will consider your local time zone and it will change the format without the reference time of the UTC. @HommerSmith – Ankit Agarwal Apr 30 '18 at 13:14
Dates do not have a timezone. The behaviour of *Date.parse* in this case is entirely implementation dependent and should not be relied on. Some browsers will return an invalid date, others will likely ignore the "Z". – RobG Apr 30 '18 at 13:15
@RobG what solution do you suggest? – Hommer Smith Apr 30 '18 at 13:17
Ok, if you want to add a solution, I will accept it. – Hommer Smith Apr 30 '18 at 13:22
I think I agree with Rob. Dates don't have a timezone, so it's weird that we add the 'Z' in the date. However, I will mark it as accepted for now, as it seems to be the best and working solution provided. – Hommer Smith Apr 30 '18 at 13:27
@AnkitAgarwal—try it in Firefox or Safari. – RobG Apr 30 '18 at 13:51

score 1 · Answer 2 · answered Apr 30 '18 at 13:00

1

I think this is to do with the locale of the machine (i.e you're on gmt+2 so 4/7/2018 at 00:00:00 is indeed 2018-04-06T22:00:00.000Z)

You could do new Date('4/7/2018 GMT').toISOString();

answered Apr 30 '18 at 13:00

Expired Data

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score -1 · Accepted Answer · answered Apr 30 '18 at 13:44

Date strings do not have a timezone. Using the built-in parser for any format other than the one specified in ECMA-262 (a limited subset of ISO 8601) is implementation dependent and should not be used, see Why does Date.parse give incorrect results?

A couple of options are to parse the string as UTC values and then use toISOString and remove the trailing Z, or you can just reformat the string, e.g.

var s = '4/7/2018';

// Parse string in m/d/y format and return
// in ISO 8601 format
function parseDMY(s) {
  var b = s.split(/\D/);
  return new Date(Date.UTC(b[2],b[0]-1,b[1])).toISOString().slice(0,19);
}

console.log(parseDMY(s));

function reformatDate(s) {
  var b = s.split(/\D/);
  function z(n){return (n<10?'0':'')+n}; 
  return `${b[2]}-${z(b[0])}-${z(b[1])}T00:00:00`;
}

console.log(reformatDate(s));

But really, if you just have a date, it should be left as just a date, so:

var s = '4/7/2018';

// Assume date is M/D/Y
function reformatDate(s) {
  var a = s.split(/\D/).map(n=>(n<10?'0':'')+n);
  return a[2]+'-'+a[0]+'-'+a[1];
}

console.log(reformatDate(s));

Rob, thanks. What do you think of this as a solution: `var timezoneOffset = new Date().getTimezoneOffset() * 60000; new Date(new Date('4/7/2018') - timezoneOffset).toISOString()` — Hommer Smith, Apr 30 '18 at 14:07
@HommerSmith—it's still using the built-in parser with an unsupported (by ECMA-262) format. — RobG, Apr 30 '18 at 21:17

Prevent toIsoString to change day

3 Answers3