Date Object

How does the JavaScript Date object work, and what are some common methods?

Dates and times in JavaScript have not always been easy to work with. In a professional codebase, you will probably be using a library that has solved a lot of those issues for you.

But there will be times where you will need to work JavaScript’s built-in Date object.

In this lecture video, we will go over the basics of the Date object and some of the most common methods that you will use when working with dates and times in JavaScript.

The Date object is a built-in object in JavaScript that allows you to work with dates and times. Here is the basic syntax for creating a new Date object:

const now = new Date();

The new keyword is used to create a new instance of the Date object, and the Date object is then assigned to the variable now. If you were to log the value of now to the console, you would see the current date and time based on the system clock of the computer running the code.

Here is an example response you would see if you logged the value of now to the console:

const now = new Date();
console.log(now);
// Mon Mar 15 2021 14:30:00 GMT-0700 (Pacific Daylight Time)

For the time, it is using the military time format, so 14:30 is 2:30 PM. GMT-0700 is the timezone offset, and Pacific Daylight Time is the timezone name.

You can also pass in a specific date and time to the Date object by providing the year, month, day, hour, minute, second, and millisecond values as arguments.

Here is an example of creating a new Date object with a specific date and time:

const specificDate = new Date("July 4, 1776 12:00:00");
 
console.log(specificDate);
// Wed Jul 04 1776 12:00:00 GMT-0700 (Pacific Daylight Time)

This is useful when you need to work with a specific date and time rather than the current date and time. The input always needs to be a string, and the format should be recognizable by the Date object.

To get the current date and time, you can use the Date.now() method, which returns the number of milliseconds since January 1, 1970, 00:00:00 UTC. This is known as the Unix epoch time.

Unix epoch time is a common way to represent dates and times in computer systems because it is an integer that can be easily stored and manipulated. UTC stands for Universal Time Coordinated, which is the primary time standard by which the world regulates clocks and time.

If you need to get a day of the month based on the current date, you can use the getDate method. Here is an example of using the getDate method:

const now = new Date();
const date = now.getDate();
console.log(date); // 15

In this example, we create a new date instance using the Date object and assign it to the variable now. We then call the getDate method on the now object to get the day of the month and assign it to the variable date. Finally, we log the value of date to the console, which will output the current day of the month.

getDate will return an integer value between 1 and 31, depending on the day of the month. If the date is invalid, it will return NaN (Not a Number).

To get the month, you can use the getMonth method like this:

const now = new Date();
const month = now.getMonth();
console.log(month);
// 2

The month is zero-based, so January is 0, February is 1, and so on. In this example, the output is 2, which corresponds to March. If the month is invalid, it will return NaN.

If you need to get the full year, then you can use the getFullYear method like this:

const now = new Date();
const year = now.getFullYear();
console.log(year);
// Output: 2024

In this example, the output is 2024, which is the current year. If the year is invalid, it will return NaN.

There are many more methods available on the Date object including getHours, getMinutes, getSeconds, and so on. I encourage you to explore some more on your own through Mozilla’s documentation or other resources.

Formatting Date