How to Properly Use :class Binding in Vue.js to Style Elements

Описание: Learn how to effectively use `:class` and `:style` bindings in Vue.js to customize the appearance of your HTML elements with dynamic classes and styles.
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This video is based on the question https://stackoverflow.com/q/77048248/ asked by the user 'nataly ren' ( https://stackoverflow.com/u/21096140/ ) and on the answer https://stackoverflow.com/a/77048288/ provided by the user 'Jaromanda X' ( https://stackoverflow.com/u/5053002/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding CSS Class Binding in Vue.js

When working with Vue.js, one common task developers encounter is styling HTML elements dynamically based on various conditions. This often involves using Vue's :class binding to apply CSS classes to elements. In this post, we will explore a common issue developers face when trying to change the background color of a paragraph using :class and explain the correct way to do it.

The Problem: Incorrect CSS Class Binding

Imagine you want to change the background color of a paragraph element to enhance its visibility. Here's how someone might initially attempt to achieve this:

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

And in your Vue instance, you might have a computed property like this:

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

While this might seem like a valid approach, it leads to some confusion. The getStyle function isn't returning a CSS class name but is trying to manipulate the DOM directly, which is not the intended use of Vue's :class binding.

The Solution: Returning a CSS Class Name

To fix this issue, the purpose of the :class binding needs to be re-evaluated. Instead of trying to manipulate styles directly, you should return a string that corresponds to a CSS class name. Here’s how you can do it:

Step 1: Define the CSS Class

First, you need to create a CSS class that will apply the desired background color:

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

Step 2: Update the Computed Property

Now, modify your computed property so that it returns the class name instead:

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

Step 3: HTML Adjustment

With the CSS class defined and the computed property returning the correct class name, your HTML will remain the same:

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

Result

Now, when Vue processes this code, it will apply the highlight class to the paragraph, resulting in the desired background color.

Alternative: Using :style Binding

If you prefer not to use classes and want to apply inline styles directly, you can use the :style binding instead. Here's how you can achieve that:

Step 1: Update the Paragraph Tag

Change your HTML to use :style binding:

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

Step 2: Modify the Computed Property

Update your computed property to return an object representing CSS properties:

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

Conclusion

Both methods—using :class with a defined class or :style with inline styles—allow you to dynamically style elements in Vue.js effectively. The choice between them depends on your specific use case and preference. Using classes is generally more maintainable, while inline styles can be more convenient for quick styling changes.

By understanding these principles, you can better manage the styles of your Vue components and create visually engaging applications.