Problem with Date timestamp on Javascript-CodePudding

I have a function that set the date to UTC 0. Like this:

const removeDateTimestamp = (date) => {
    return new Date(
        date.getUTCFullYear(),
        date.getUTCMonth(),
        date.getUTCDate(),
        0,
        0,
        0,
        0
    );
};

But the problem is when I use it. If I use on my console on the browser I get this result:

Sat May 15 2021 00:00:00 GMT 0200 (hora de verano de Europa central)

But when I run tests on Jest I got this other result:

Received has type:  date
Received has value: 2021-05-14T22:00:00.000Z

it("removeDateTimestamp", () => {
expect(removeDateTimestamp(new Date(2021, 4, 16))).toMatch(
    /2021-05-16T00:00:00.000Z/i
  );
});

In the first example I have Sat May 15 2021 00:00:00 GMT 0200 when the passed day is 16, and in the second example with same day is 14.

I'm clearly overlooking something important but I don't see it.

CodePudding user response：

The Date constructor interprets its arguments in local time. To get a Date instance from parts using UTC, use Date.UTC (which returns a milliseconds-since-The-Epoch value, so if you want a Date instance, you pass the result to new Date):

const removeDateTimestamp = (date) => {
    return new Date(
        Date.UTC(
            date.getUTCFullYear(),
            date.getUTCMonth(),
            date.getUTCDate(),
            0,
            0,
            0,
            0
        )
    );
};

FWIW, here's another way to do the same thing you're doing above:

const removeDateTimestamp = (date) => {
    const newDate = new Date( date); // Clone the date -- the ` ` is important
                                     // on some JavaScript engines
    newDate.setUTCHours(0, 0, 0, 0);
    return newDate;
};

I should also mention there's a way to do this with the new Temporal API that will be making its way into the standard library soon (already at Stage 3).

CodePudding user response：

T.J. has the detailed answer and I can't find a suitable duplicate so I'll post this as a simplification that fixes your issue.

Since ECMAScript days always have exactly 8.64e7 ms, you can just subtract the remainder after dividing by ms in one day, e.g.

const getUTCTimeZero = (date) => new Date(date - date % 8.64e7);

console.log(getUTCTimeZero(new Date()))

The name removeDateTimestamp is a bit misleading as a timestamp is any string or number (or value perhaps) that represents a date or time. You seem to just want to set the time to zero, hence the different name.