There’s no escaping the clock, especially in programming. Just as we rely on clocks and watches to keep track of our days, so do programs use time-tracking tools to know what should happen and when.
Several applications need to track time. A blog application needs to remember when a post was created, whereas a calendar application displays your scheduled events.
The date object looks like this:
How to Use the Date Object
Without any values, the Date object tells us the current date and time. This is calculated based on your operating system’s settings and taking your timezone into account.
We can use the Date object to retrieve the current date, like this:
var currentDate = new Date(); console.log(currentDate);
Our code returns a Date object which contains the following values:
Wed Jun 24 2020 10:49:46 GMT+0100 (British Summer Time)
As you can see, this article was written in the UK on June 24, 2020, as our timestamp shows. The beauty of the Date object is that it returns data in a human-readable date format so that it is easy for us to understand.
Retrieving a Timestamp Using Date
To retrieve the current time as a timestamp, you can use the
var currentDate = new Date(); console.log(currentDate.getTime());
Our code returns
Creating a Date Object
The default value of the Date object is the current date and time. You can change this to create a date based on a particular timestamp or date and time.
You can do this by specifying either a timestamp, a date string, or a set of numbers that correspond to the current date and time:
- new Date(timestamp)
- new Date(string)
- new Date(year, month, day, hours, minutes, seconds, number of milliseconds)
Suppose we want to create a timestamp for January 1, 2021. We could do so using this code:
var nextYear = new Date("January 1 2021 12:00"); console.log(nextYear);
Our code returns: Fri Jan 01 2021 12:00:00 GMT+0000 (Greenwich Mean Time)
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We could also have created this timestamp using these lines of code:
var nextYear = new Date(1609502400000); console.log(nextYear); var nextYear = new Date(2021, 1, 1, 0, 0, 0, 0); console.log(nextYear);
Our code returns:
Fri Jan 01 2021 12:00:00 GMT+0000 (Greenwich Mean Time) Fri Jan 01 2021 12:00:00 GMT+0000 (Greenwich Mean Time)
All of these methods create the same Date object.
Retrieving the Date
The Date object comes with an array of built-in methods to access particular pieces of information about the date. The methods that allow you to retrieve information about the date start with
get. Here’s a list for your reference:
- Year: getFullYear()
- Month: getMonth() (between 0 and 11, where 0 is January)
- Day of the Month: getDate() (between 1 and 31)
- Day of the Week: getDay() (between 0 and 6, where Sunday is 0)
- Hour: getHours() (between 0 and 23, where midnight is 0)
- Minute: getMinutes()
- Second: getSeconds()
- Millisecond: getMilliseconds()
- Timestamp: getTime()
Let’s say we want to find out what time it is right now. We could do so using this code:
const currentDate = new Date(); console.log(currentDate.getHours());
Our code returns
11. This shows us that it’s currently 11 hours into the day.
These functions are useful because they help us extract specific pieces of information about the day. We don’t need to worry about manipulating any strings; we can just use the
get methods to learn more about the current time.
You can retrieve a timestamp using Universal Time Coordinated (UTC) by adding
UTC between the word
get and the date value. By default, the Date object will return information in a user’s local timezone. If you are working with users in multiple time zones, it’s often best to use UTC to track the time events happen easily.
Updating a Date Object
Date objects can be updated using the Date
set methods. There is a
set method for every
get method offered by the Date object:
- Year: setFullYear()
- Month: setMonth()
- Day of the Month: setDate()
- Day of the Week: setDay()
- Hour: setHours()
- Minute: setMinutes()
- Second: setSeconds()
- Millisecond: setMilliseconds()
- Timestamp: setTime()
Suppose we want to find out what day of the week it was on this date last year. We could do so by setting the year on our Date object to 2019 using
setFullYear(). Then, we can use
getDay() to retrieve the day of the week:
const currentDate = new Date(); currentDate.setFullYear(2019); const daysOfTheWeek = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', Saturday', Sunday']; const dayLastYear = currentDate.getDay(); console.log('On this day last year it was ' + daysOfTheWeek[dayLastYear]);
Our code returns: On this day last year it was Tuesday.
We first use
Date() to retrieve the current date. We then use the
setFullYear() method to set the year on our date object to 2019.
Next, we declare an array called
daysOfTheWeek. This helps us convert the number returned by
getDay() into a day of the week.
We then use the
getDay() method to figure out what day of the week it was this time in 2019. Then, we print out the message
On this day last year it was followed by the day of the week.
get methods which help you learn about the current time and