How to assume new Date(YYYY-MM-DD) input is UTC date

Question

I need to generate a javascript Date from a UTC date string with the format YYYY-MM-DD. Here is an example:

var date = new Date('2018-01-31');

The date this creates is:

Tue Jan 30 2018 19:00:00 GMT-0500 (Eastern Standard Time)

Given the time zone offset, the date is yesterday.

How can I create a javascript Date that assumes the timeless input is UTC?

Answer 1

You can use Date.UTC .
This is an example from https://developer.mozilla.org/de/docs/Web/JavaScript/Reference/Global_Objects/Date/UTC

var utcDate1 = new Date(Date.UTC(96, 1, 2, 3, 4, 5));
var utcDate2 = new Date(Date.UTC(0, 0, 0, 0, 0, 0));

console.log(utcDate1.toUTCString());
// expected output: Fri, 02 Feb 1996 03:04:05 GMT

console.log(utcDate2.toUTCString());
// expected output: Sun, 31 Dec 1899 00:00:00 GMT

So you get this as solution:

var test = "2018-01-31";
var year = test.substr(0,4);
var month =  test.substr(5,2) -1;
var day =  test.substr(8,2);

var utcDate1 = new Date(Date.UTC(year,month,day));
alert(utcDate1.toUTCString());
// expected output:Wed, 31 Jan 2018 00:00:00 GMT

Answer 2

You can use a combination of Date.UTC, split and the spread operator syntax (... is not an operator):

var convertedDate = '2018-01-31'.split('-');
convertedDate[1] = convertedDate[1] - 1 // Date.UTC expects a value from 0-11

var date = new Date(Date.UTC(...convertedDate))
console.log(date.toDateString());

It is important to note that Date.UTC expects a month form 0-11 (for some reason)