Скачать или смотреть How to Subtract CSS Left Value Using JavaScript with Percentages

Learn how to manipulate the CSS `left` property using JavaScript to subtract values in percentages effectively.
---
This video is based on the question https://stackoverflow.com/q/62648157/ asked by the user 'Kamil Rzeszutek' ( https://stackoverflow.com/u/12071398/ ) and on the answer https://stackoverflow.com/a/62665460/ provided by the user 'Kamil Rzeszutek' ( https://stackoverflow.com/u/12071398/ ) 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: Subtract css left value using javascript

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.
---
Subtract CSS Left Value Using JavaScript with Percentages

When working with web development, you might encounter situations where you need to dynamically adjust the positioning of elements on your webpage. If you're looking to subtract the CSS left value using JavaScript but want to use percentages instead of pixels, you're not alone! This is a common challenge that can be tricky to resolve. In this guide, we’ll walk through the problem and provide clear solutions to get your element moving just how you want.

The Problem: Adjusting CSS Left Value

Your goal is to adjust the position of an element, such as a circle, by decrementing its left position in percentage increments every time a user presses the left arrow key. Initial CSS for your element might look something like this:

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

As this code indicates, the .fa-circle starts at a left position of 50%. When the left arrow key (key code 37) is pressed, you want to decrease that value. But here’s the catch: directly manipulating percentage values presents some challenges when it comes to browser calculations.

The Challenge: Working with Percentages

Initially, you might think to simply subtract a percentage from the current position like this:

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

However, this approach can lead to unintended results since JavaScript will calculate the percentage based on its current pixel value, which could lead to incorrect positioning.

The Solution: Correctly Subtracting Percentage Values

To properly subtract a fixed percentage from the left position, we will need to do some calculations instead of directly using CSS methods that do not translate percentages accurately to pixels. Here’s a step-by-step breakdown of how to achieve this:

Step 1: Capture the Current Left Position

You'll first want to grab the current left percentage value and convert it from pixels to a usable format for calculation:

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

Step 2: Calculate the New Value

Instead of directly subtracting 3%, you will calculate 3% of the window.innerWidth to ensure that the calculated movement is appropriate based on the viewport size:

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

Step 3: Adjust the CSS Left Value

Now, you can subtract this calculated width from the current left position:

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

Complete Code Solution

Here’s the complete code that achieves the desired functionality:

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

Conclusion

By utilizing the calculations based on window.innerWidth, this method ensures you correctly adjust the left position of your element by a consistent 3% rather than risking discrepancies introduced by pixel-based calculations.

With this guide, you should now be able to manage CSS positioning with precision and achieve smooth interactions in your web applications. Happy coding!