Скачать или смотреть How to Accurately Calculate the Number of Months Between Two Dates in TypeScript

Learn how to effectively calculate the number of months between two dates, considering complications such as differing days in months and time of day factors using TypeScript and Moment.js.
---
This video is based on the question https://stackoverflow.com/q/67665072/ asked by the user 'javaistaucheineinsel' ( https://stackoverflow.com/u/13919748/ ) and on the answer https://stackoverflow.com/a/67665267/ provided by the user 'theKunz' ( https://stackoverflow.com/u/3317285/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: calculate how many months in a time period

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Accurately Calculate the Number of Months Between Two Dates in TypeScript

Calculating the number of months between two dates can be more complicated than it initially seems. If you’ve been using libraries like Moment.js in TypeScript for your date manipulations, you may have encountered unexpected results that don’t align with your expectations, especially when working with incomplete months. In this post, we’ll explore how to solve this issue effectively.

The Problem Statement

Suppose you have two dates, start and end, and you want to determine how many complete months lie between these dates, inclusive. For example:

Contract Start: 01.05.2021

Contract End: 31.05.2021

When attempting to calculate the months using Moment.js, you might expect the output to be 1 since there is one complete month between the two dates. However, the result you might get is a decimal value, such as 0.9856465225158627. This raises the question: Why are we getting a fractional value instead of a whole number?

Understanding the Calculation

Time of Day Matters

One of the primary reasons for the discrepancy is the inclusion of the time component when calculating duration. If both the start and end date times are not aligned (e.g., starting at noon and ending at 11:59 PM), the calculation may yield a fractional month.

Example:

If the start time is noon on the 1st and the end time is just before midnight on the 31st, the duration is technically 30 days, but since the month ends at 31 days, you will receive a result less than one full month.

Days in a Month Vary

Another key factor is that months vary in the number of days they contain (28, 30, or 31 days). When Moment.js calculates the number of months, it does not treat each month uniformly.

For instance:

The code snippet found in Moment.js calculates the average days in a month based on a complex formula that factors in leap years:

[[See Video to Reveal this Text or Code Snippet]]

This means that 31 days actually exceeds the length of an entire month when averaged out over a lengthy period, leading to the decimal value returned.

Proposed Solutions

To overcome these issues, consider the following strategies:

1. Use isSame and isAfter Checks

To include both start and end dates, you can set up logical checks:

[[See Video to Reveal this Text or Code Snippet]]

2. Rounding the Result

If you prefer the previous method’s approach but still want whole numbers, consider rounding:

[[See Video to Reveal this Text or Code Snippet]]

3. Using a Custom Function

Create a custom function to handle various edge cases, ensuring you account for inclusion of dates and varying month lengths.

Conclusion

Calculating complete months between two dates in TypeScript using Moment.js requires an understanding of both time components and the nuances of calendar discrepancies. By implementing proper checks and using rounding or custom functions, you can achieve the accurate month count needed for your projects. Now, you can calculate the number of months confidently!

Feel free to share any additional tips or methods you might have for date calculations in the comments below!