Borislav Hadzhiev
Thu Jan 27 2022·2 min read
Photo by Meiying Ng
To get the day of the year:
function getDayOfYear(date = new Date()) { const timestamp1 = Date.UTC( date.getFullYear(), date.getMonth(), date.getDate(), ); const timestamp2 = Date.UTC(date.getFullYear(), 0, 0); const differenceInMilliseconds = timestamp1 - timestamp2; const differenceInDays = differenceInMilliseconds / 1000 / 60 / 60 / 24; return differenceInDays; } console.log(getDayOfYear(new Date('2022-02-01'))); // 👉️ 32 console.log(getDayOfYear(new Date('2022-01-29'))); // 👉️ 29 console.log(getDayOfYear(new Date('2022-03-01'))); // 👉️ 60 console.log(getDayOfYear(new Date('2022-12-31'))); // 👉️ 365
We created a reusable function that returns the number of the day of the year.
The function takes a Date
object as a parameter or uses the current date if
none is provided
The
Date.UTC
method takes similar parameters to the Date()
constructor, but treats them as
UTC and returns the number of milliseconds since the 1st of January 1970,
00:00:00 UTC.
Date.UTC
method to avoid any Daylight Saving Time (DST) issues.In the first call to the method, we got a timestamp of the passed in date.
We used the following 3 date-related methods:
Date.getFullYear method - returns a four-digit number representing the year that corresponds to a date.
Date.getMonth -
returns an integer between 0
(January) and 11
(December) and represents
the month for a given date. Yes, unfortunately the getMonth
method is off
by 1
.
Date.getDate -
returns an integer between 1
and 31
representing the day of the month for
a specific date.
In our second call to the Date.UTC()
method, we got a timestamp for the last
day of the previous year.
We passed 0
for the month of January and 0
for the day.
Note that the value for the day of the month is not zero-based, it is one-based.
Date
object in JavaScript automatically takes care of rolling back or rolling over the values for the month and year, so we got a timestamp for the last day of the previous year.Subtracting the second timestamp from the first, gives us the difference between the passed in date and the last day of the previous year in milliseconds.
The last step is to convert the difference from milliseconds to days to get the day of the year.