How To Get The Week Number Based On A Specific Day In Moment.js?

When working with dates, you might need to determine the week number based on a specific day. Moment.js provides several methods to achieve this, whether you want to use built-in functions like week() or isoWeek(), or prefer a custom calculation approach.

Run the below command before running the code in your local system:

npm i moment

These are the approaches to get the week number based on a specific day in Moment.js:

Using week() Method

In this approach, we are using Moment.js's week() method to directly retrieve the week number of a specific date. By providing the desired date to Moment.js, the week() method calculates and returns the corresponding week number based on the date.

Example: The below example uses the week() Method to get the week number based on a specific day in Moment.js.

Output:

Input Date: 2024-08-22
Week Number: 34

Using isoWeek() Method for ISO Week

In this approach, we are using Moment.js's isoWeek() method to obtain the ISO week number of a specific date. The isoWeek() method follows the ISO 8601 standard, where the week starts on Monday and the first week of the year contains the first Thursday. This method returns the ISO-compliant week number based on the given date.

Example: The below example uses the isoWeek() Method for ISO Week to get the week number based on a specific day in Moment.js.

Output:

Input Date: 2024-08-22
ISO Week Number: 34

Custom Calculation Using dayOfYear() and Arithmetic

In this approach, we are using Moment.js's dayOfYear() method and custom arithmetic to manually calculate the week number. First, we determine the number of days since the start of the year, then adjust this value by adding the day of the week and dividing by 7 to calculate the week number. The Math.ceil function ensures that the week number is correctly rounded up.

Example: The below example uses the Custom Calculation Using dayOfYear() and Arithmetic to get the week number based on a specific day in Moment.js.

Output:

Input Date: 2024-08-22
Calculated Week Number: 34