Day 12: Classes

Lesson 5: Date()

So why did we bother learning about classes then? Mainly because of the JavaScript Date class which is very useful and important to understand how to use.

The Date class is pretty big and involved, it has a lot of instance and class methods. Don't worry though we're not going to do a full deep dive. I'm just going to show you most common use cases.

Like all classes, you get a new Date by calling it's constructor

<h1>Hello World<h1>

const now = new Date();
console.log(now);

Now, while that looks like now is just a string, it's not. What's happened is that console.log() has printed out the default human readable date time.

We can prove that it's not just a simple string by calling an instance method on now. And boy are there a lot of instance methods you can call on a Date. Here are just a few.

<h1>Hello World<h1>

const now = new Date();
console.log(now.getFullYear());
console.log(now.getHours());
console.log(now.getTimezoneOffset());

None of these should be a surprise to you. But this one might be.

<h1>Hello World<h1>

const now = new Date();
console.log(now.getTime());

Probably a bigger number than you were expecting right? Well, this is the number of milliseconds since midnight on January 1st 1970 UTC time. This is called 'Unix Epoch time' and can be thought of as the start of computer time if you like.

Thanks to leap years, leap seconds and time zones, dates and times are one of the biggest headaches in programming. Being able to get a single number timestamp dating back to a universally agreed point in time is very, very useful.

In fact it's common and useful that there is class (static) method to get it without creating a Date first.

<h1>Hello World<h1>

const now = Date.now();
console.log(now);

If you want to create a Date at a specific date you can do that with by passing a date into your Date constructor.

<h1>Hello World<h1>

const millennium = new Date("1 Jan 2000 00:00:00 UTC");
console.log(millennium);

There's a lot more to dates than this, the best place to learn more about the Date class is the MDN Docs when you need to work with them more.