JavaScript’s Date does not stop to amaze me.
Probably every developer has encountered lots of problems when working with it.
Most projects use other date libraries like Moment.js or JS-Joda to cope with its shortcomings.
In case you want to or have to stick to JavaScript’s Date here are some things I find useful to remember.

A Date object can be created several ways. Here are the most popular ones:

const d1 = new Date(1692967999168);
const d2 = new Date('2023-08-25T12:53:19.168Z');
const d3 = new Date(2023, 7, 25, 12, 53, 19, 168);Code-Sprache: JavaScript (javascript)

Every created date refers to the same date in time:

[d1, d2, d3].map(d => d.toISOString())
// results in
[
    "2023-08-25T12:53:19.168Z",
    "2023-08-25T12:53:19.168Z",
    "2023-08-25T10:53:19.168Z"
]Code-Sprache: JavaScript (javascript)

Why did I use toISOString and not toString?

The answer is that toISOString always uses the UTC time-zone and toString uses your browser’s local time-zone.

If you want to compare dates always use toISOString.

This means that a date object is always both: a local date and an UTC-date.

In case you want to retrieve the UTC-related information from the date object, Date provides certain functions for that: getUTCHours, getUTCMonth and so on.

If you want the same information for your browser’s local time-zone you may use getHours, getMonth and so on.

Unfortunately, there is no way (so far) to easily retrieve the same information for a time-zone that is neither UTC nor your browser’s time-zone.

However, if you just want to format the date in a certain time-zone, that can be done using the Intl.DateTimeFormat:

console.log(
  new Intl.DateTimeFormat('en-GB', { dateStyle: 'full', timeStyle: 'long', timeZone: 'Australia/Sydney' }).format(new Date(1692967999168)),
);
// result: Friday, 25 August 2023 at 22:53:19 GMT+10Code-Sprache: JavaScript (javascript)

Use Intl.DateTimeFormat to format a date with a certain time-zone.

Sometimes you may encounter invalid date-objects. That may happen on purpose or by accident (e.g. an invalid user input).

An invalid date-object is still an object of type Date but you may run into errors if you try to do something useful with it:

new Date('13-13-13').toISOString();
// will throw: Uncaught RangeError: Invalid time value at Date.toISOStringCode-Sprache: JavaScript (javascript)

Fortunately, there is an easy way to detect an invalid date. Calling getTime on an invalid date will return NaN (not a number):

const invalidDate = new Date('13-13-13');
const timestamp = invalidDate.getTime();
Number.isNaN(timestamp); // evaluates to true!Code-Sprache: JavaScript (javascript)

getTime will evaluate to Number.NaN if the date is invalid.

This implies that you can create an invalid date with new Date(Number.NaN).

Well folks, that’s it so far. I hope you can use some of the provided insights.

Let me know if you find a bug or want something to be added.

Until then, happy coding!