Calculate current week number in JavaScript
The week number indicates the number of weeks that have been completed in the current year.
Example:
The week number of january 1 = week 1 The week number of january 30 = week 5
Explanation: From the below calendar we can see that Jan 1 is in week 1 and Jan 30 in week 5
In the process of calculating the current week’s number, we will the following numbers.
JavaScript getFullYear() Method: The getFullYear() returns the full year (4 digits) of a date.
Syntax:
Date.getFullYear()
JavaScript getDay() Method: The getDay() method returns the day of the week (0 to 6) of a date.
Syntax:
Date.getDay()
Approach: Initialize the current date to a variable using a new Date() which by default returns the current date. Initialize the starting date of the current year ( i.e. Jan 1) to startDate. Calculate the difference between the two dates in days by subtracting startDate from currentDate.
- This returns the difference between dates in milliseconds.
- now dividing the result by the total milliseconds in a day gives a difference between dates in days.
Add the number of days to the current weekday using getDay() and divide it by 7. We will get the current week’s number.
Example: Below code will illustrate the above example:
Javascript
currentDate = new Date();startDate = new Date(currentDate.getFullYear(), 0, 1);var days = Math.floor((currentDate - startDate) /Â Â Â Â (24 * 60 * 60 * 1000));Â
var weekNumber = Math.ceil(days / 7);Â
// Display the calculated result      console.log("Week number of " + currentDate +    " is :  " + weekNumber); |
Output:
Week number of Fri Dec 30 2022 13:53:43 GMT+0530 (India Standard Time) is : 52
