How to Subtract Dates to Get the Number of Years in JavaScript

Описание: Learn how to effectively subtract dates in JavaScript to calculate the number of `years` between them with ease!
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This video is based on the question https://stackoverflow.com/q/67269906/ asked by the user 'Jack Yuan' ( https://stackoverflow.com/u/15691137/ ) and on the answer https://stackoverflow.com/a/67270642/ provided by the user 'Kinglish' ( https://stackoverflow.com/u/1772933/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Subtract Dates to Get the Number of Years in JavaScript

Calculating the difference between two dates can be crucial in various applications, whether it's for age calculations, project timelines, or even interest calculations. If you’ve been trying to figure out how to subtract dates to obtain the number of years using JavaScript but faced difficulties, you're not alone. In this post, we’ll walk through the problem and provide you a solid solution to make this task straightforward.

Understanding the Problem

The issue arises when trying to subtract two dates represented by HTML input fields of type date. The initial attempt uses the following code:

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

In the code above, the logic isn't working because the val() method returns a string formatted as yyyy-mm-dd, and applying the unary plus operator + doesn’t result in the desired numeric value for date subtraction. Let’s explore a better way to accomplish this.

A Step-by-Step Guide to Subtract Dates

Step 1: Update the Input Types

First, we need to change the input for totalyears from type='date' to type='text'. This allows us to display a calculated value rather than a date selection. Here’s how your HTML input fields should look now:

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

Step 2: Implement the JavaScript Logic

Instead of trying to subtract the dates directly as strings, we need to convert them to Date objects and compute the difference in milliseconds. We can then convert that difference to years. Here’s the refined JavaScript code:

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

Why This Works

Date Conversion: Using new Date(value) converts the date string into a Date object, allowing for accurate date calculations.

Milliseconds Calculation: getTime() returns the number of milliseconds since January 1, 1970, 00:00:00 UTC, which makes it easy to calculate time differences.

NaN Check: We ensure that we only perform calculations when both dates are valid to avoid errors in our output.

Displaying Results: The result is formatted to two decimal points for clarity and precision.

Conclusion

With these steps, you’ll easily be able to subtract dates and find the number of years between them using JavaScript. This practice can be valuable in diverse fields and enhances user interaction within your applications. Remember the crucial adjustments in both HTML and JavaScript, and feel free to adapt the code to fit into your projects. Happy coding!