How To Calculate Weeks Between Two Dates In Javascript

Calculating the number of weeks between two dates is a common task in JavaScript development. This tutorial will show you step-by-step how to do this using native JavaScript functions and the popular Moment.js library.

Step 1: Create two date objects

First, create two Date objects for the two dates you want to compare. If you have the dates in the form of strings, you can easily create a date object using the Date constructor:

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const date1 = new Date("2022-01-01");
const date2 = new Date("2022-12-31");

Step 2: Calculate the number of milliseconds between the two dates

To calculate the differences between the two dates, get the time (in milliseconds) for each date using the getTime() method and subtract the values:

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const timeDifference = date2.getTime() - date1.getTime();

Step 3: Convert the milliseconds difference to weeks

Now convert the time difference in milliseconds to weeks. Since there are 1000 milliseconds in a second, 60 seconds in a minute, 60 minutes in an hour, 24 hours in a day, and 7 days in a week, you should divide the time difference by the product of these values:

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const weeksDifference = timeDifference / (1000 * 60 * 60 * 24 * 7);

To round the result, use the Math.round(), Math.floor(), or Math.ceil() function, depending on your rounding requirements:

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const roundedWeeksDifference = Math.round(weeksDifference);

Output:

Number of weeks between 2022-01-01 and 2022-12-31: 52

Using Moment.js

If you prefer using the Moment.js library, follow these steps:

Step 1: Include Moment.js in your project

First, include the Moment.js library in your project using a script tag, or run npm install moment if you’re using Node.js.

Step 2: Create two moment objects

Create two moment objects for the two dates you want to compare:

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const moment1 = moment("2022-01-01", "YYYY-MM-DD");
const moment2 = moment("2022-12-31", "YYYY-MM-DD");

Step 3: Calculate the number of weeks difference between the two moment objects

Use the diff() method provided by Moment.js to calculate the difference in weeks between the two moment objects:

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const weeksDifference = moment2.diff(moment1, "weeks");

Output:

Number of weeks between 2022-01-01 and 2022-12-31: 52

Full code:

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// Using native JavaScript
const date1 = new Date("2022-01-01");
const date2 = new Date("2022-12-31");
const timeDifference = date2.getTime() - date1.getTime();
const weeksDifference = timeDifference / (1000 * 60 * 60 * 24 * 7);
const roundedWeeksDifference = Math.round(weeksDifference);
console.log(roundedWeeksDifference);
 
// Using Moment.js
const moment1 = moment("2022-01-01", "YYYY-MM-DD");
const moment2 = moment("2022-12-31", "YYYY-MM-DD");
const weeksDifferenceMoment = moment2.diff(moment1, "weeks");
console.log(weeksDifferenceMoment);

Conclusion

Calculating the weeks between two dates is a common task in JavaScript, and it can be done using either native JavaScript functions or by using the Moment.js library. Choose the method that suits your project requirements and coding style.