Скачать или смотреть How to Dynamically Append Classes Using JavaScript

A comprehensive guide on how to dynamically append classes in your HTML elements using vanilla JavaScript, perfect for handling user input error states.
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This video is based on the question https://stackoverflow.com/q/63549928/ asked by the user 'Daniel' ( https://stackoverflow.com/u/6719819/ ) and on the answer https://stackoverflow.com/a/63550049/ provided by the user 'kmoser' ( https://stackoverflow.com/u/378779/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Dynamically Append Classes in JavaScript: A Step-by-Step Guide

In web development, ensuring that users interact with forms in an intuitive manner is crucial. One common challenge developers face is managing the visual feedback of form fields, particularly when users leave fields empty. This can often result in confusion and frustration. In this guide, we will walk through a practical example of how to dynamically append classes to HTML elements using JavaScript, specifically to indicate error states for an input field.

The Problem

Imagine we have a simple form containing an input field that should visually signify an error if the user clicks out of the input without entering any text. The structure of our HTML looks like this:

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

Default CSS Styles

The default styles applied to this input field through CSS look like this:

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

When a user leaves the input field without entering anything, we want to apply an error state, adding a red border around the input element:

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

The Solution: JavaScript Code Implementation

To implement this functionality, we will use two event listeners in JavaScript that will manage the addition and removal of the "error" class.

Step 1: Focus Event Handling

When the input field gains focus, we want to remove any existing error class. This gives visual feedback to the user that they are actively editing the input. We achieve this with the following code:

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

Step 2: Blur Event Handling

When the input field loses focus (i.e., the user clicks outside), we need to check if it’s empty or filled. Based on this, we will either add or remove the error class:

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

Conclusion

By following these steps, you can effectively manage user input feedback in your web forms. Utilizing event listeners to add and remove classes dynamically allows for a more interactive and user-friendly experience. This simple yet effective technique can significantly enhance the usability of forms on your website.

Don't hesitate to adopt similar approaches in your projects to ensure clarity and improve user experience. Happy coding!