How to use is() Property in CSS
Tags: css, tutorial, html, ui
Published: 2024-06-14 09:46:55

In the ever-evolving world of web development, CSS remains a fundamental language for crafting visually appealing user interfaces. Among the myriad of selectors and properties CSS offers, the `is()` function stands out as a potent tool that every UI developer should master. This article delves into the nuances of the `is()` property, exploring its functionalities, use cases, and best practices to elevate your CSS skills.

### Introduction: Why the `is()` Property Matters

As a UI developer, you continuously search for ways to make your CSS more efficient and readable. The `is()` property, introduced in CSS Selectors Level 4, offers a streamlined approach to writing complex selectors. At its core, `is()` allows you to consolidate multiple selectors into a single, easier-to-read expression, simplifying your CSS and enhancing maintainability.

But what exactly is the `is()` property, and how can it transform your CSS writing experience? In this comprehensive guide, we will unpack everything you need to know about `is()`, from its syntax and practical applications to advanced techniques and potential pitfalls. By the end of this article, you'll be well-equipped to incorporate the `is()` property into your CSS toolkit, creating cleaner, more robust code.

### Unpacking the is() Property

#### What is the is() Property?
The `is()` property, also known as the "matches-any" pseudo-class, is a CSS selector function that enables you to group multiple selectors together. This means that you can target elements that match any of the selectors within the `is()` function. The syntax is straightforward:

Example
```css
element:is(selector1, selector2, selector3) {
  /* CSS rules */
}
```
In this context, `element` is the base element you want to style, and `selector1`, `selector2`, `selector3` are the individual selectors that you want to combine. The `is()` function checks each selector and applies the CSS rules if any of them match.

#### The Syntax: A Closer Look

Understanding the syntax of `is()` is crucial for leveraging its power effectively. Let's break down the basic structure:

```css
/* Basic usage */
element:is(selector1, selector2, selector3) {
  property: value;
}

/* Example */
button:is(:hover, :focus) {
  background-color: blue;
}

```

In this example, the `button` element will have a blue background color when it is either hovered over or focused, demonstrating the utility of `is()` in combining pseudo-classes.

**The Compatibility Factor**

Before diving deeper, it's essential to consider browser compatibility. The `is()` property is relatively new, so ensuring that it's supported in the browsers your users are likely to use is crucial. As of now, modern browsers such as Chrome, Firefox, Safari, and Edge support the `is()` property, making it a reliable choice for contemporary web development.


### Practical Applications of the `is()` Property

**1. Streamlining Complex Selectors**

One of the most significant advantages of the `is()` property is its ability to simplify complex selectors. Traditionally, combining selectors can result in convoluted code that's difficult to read and maintain. With `is()`, you can consolidate these selectors into a more comprehensible format.


Consider a navigation menu with various states such as `hover`, `focus`, and `active`. Without `is()`, you might write something like this:

Example
```css
nav a:hover,
nav a:focus,
nav a:active {
  color: red;
}
```

Using the `is()` property, you can streamline this to:

```css
nav a:is(:hover, :focus, :active) {
  color: red;
}
```
This approach not only reduces redundancy but also enhances readability, making your CSS easier to maintain.


**2. Enhancing Specificity Control**

Specificity often poses challenges in CSS, especially when dealing with nested elements and inheritance. The `is()` property can help manage specificity by providing a clear and concise way to target elements based on multiple conditions.



Suppose you want to apply a border to input fields, textareas, and select boxes when they are focused. Here's how you can achieve this using `is()`:

Example

```css
form :is(input, textarea, select):focus {
  border: 2px solid green;
}

```
This selector ensures that all form elements specified will receive the same styling when focused, without writing repetitive rules for each element type.


**3. Cleaner Code with HTML5 Tags**

With the introduction of HTML5, new semantic tags such as section, `article`, `aside`, and `nav`have become commonplace. These tags improve accessibility and SEO but can also lead to verbose CSS. The `is()` property offers a solution to this by allowing you to target multiple semantic tags simultaneously.

Example

```css
:is(section, article, aside, nav) {
  margin: 20px;
}
```
If you want to apply margins to several semantic containers uniformly, you can utilize the `is()` property as follows:

This method ensures consistency across all specified elements with minimal code.

### Advanced Techniques with the `is()` Property

**1. Combining is() with Other Pseudo-Classes**

The true potential of the `is()` property emerges when you combine it with other pseudo-classes and pseudo-elements. This allows for more granular control and sophisticated styling strategies.

Example
```css
form :is(input, textarea, select):invalid {
  border: 2px solid red;
}
```

Imagine creating a form where invalid inputs need to be highlighted. You can combine `is()`with the `:invalid` pseudo-class to achieve this:

By doing so, you ensure that all specified form fields receive the same error styling without redundancy.

**Nesting `is()` for Complex Scenarios**

In some cases, you may encounter scenarios where nesting `is()` within other selectors can simplify your code even further. However, it's essential to use this technique judiciously to avoid overcomplicating your CSS.

Example

```css
nav > ul > :is(li):hover > ul {
  display: block;
}
```
This selector targets the second-level unordered lists within a navigation menu, showing them when their parent list items are hovered over.

### Best Practices for Using the `is()` Property

**Keep It Readable**
While the `is()` property offers powerful capabilities, it's crucial to maintain readability. Overusing or nesting `is()` excessively can lead to convoluted CSS that defeats the purpose of simplification.

**Test Across Browsers**
Despite its support in modern browsers, always test your CSS across different browsers to ensure consistent behavior. This practice is especially important for websites with diverse user bases.

**Leverage Preprocessors**
If you're using a CSS preprocessor like SASS or LESS, you can combine `is()` with variables and mixins for added flexibility and maintainability. This approach allows for more dynamic and reusable code.

**Over-Nesting and Complexity**

As with any powerful tool, there's a risk of overcomplicating your CSS with excessive nesting. Always strive for balance and readability. If a selector becomes too complex, consider breaking it down or re-evaluating your approach.

### Conclusion: Elevate Your CSS with `is()`

The `is()` property is a valuable addition to any UI developer's toolkit. By enabling the consolidation of multiple selectors and enhancing specificity control, `is()` can streamline your CSS, making it more efficient and maintainable. Embrace this powerful feature to create cleaner, more robust stylesheets that stand the test of time.

> Mastering the `is()` property in CSS is not just about writing less code—it's about writing better, more sustainable code. 

So go ahead, experiment with `is()`, and take your CSS skills to the next level! Whether you're simplifying complex selectors, enhancing specificity, or combining it with other pseudo-classes, `is()` opens up a world of possibilities for modern UI development.