A Bare-Bones Approach to Versatile and Reusable Skeleton Loaders

This content originally appeared on CSS-Tricks and was authored by Adrian Bece

UI components like spinners and skeleton loaders make waiting for a page load less frustrating and might even affect how loading times are perceived when used correctly. They won’t completely prevent users from abandoning the website, but they might encourage them to wait a bit longer. Animated spinners are used in most cases since they are easy to implement and they generally do a good enough job. Skeleton loaders have a limited use-case and might be complex to implement and maintain, but they offer an improved loading experience for those specific use-cases.

I’ve noticed that developers are either unsure when to use skeleton loaders to enhance the UX or do not know how to approach the implementation. More common examples of skeleton loaders around the web are not all that reusable or scalable. They are usually tailor-made for a single component and cannot be applied to anything else. That is one of the reasons developers use regular spinners instead and avoid the potential overhead in the code. Surely, there must be a way to implement skeleton loaders in a more simple, reusable, and scalable way.

Spinner elements and skeleton loaders

A spinner (or progress bar) element is the simplest and probably most commonly used element to indicate a loading state. A spinner might look better than a blank page, but it won’t hold user’s attention for long. Spinners tell the user that something will load eventually. Users have to passively wait for content to load, meaning that they are unable to interact with other elements on the page or consume any other content on the page. Spinners take up the entire screen space and no content is available to the user.

However, skeleton loaders (or skeleton screens) tell the user that the content is about to load and they might provide a better loading UX than a simple spinner. Empty boxes (with a solid color or gradient background) are used as a placeholder for the content that is being loaded. In most cases, content is gradually being loaded which allows users to maintain a sense of progress and perception that a page load is faster than it is. Users are actively waiting, meaning that they can interact with the page or consume at least some part of the content while the rest is loading.

It’s important to note that loading components should not be used to address performance issues. If a website is experiencing performance issues due to the problem that can be addressed (un-optimized assets or code, back-end performance issues, etc.), they should be fixed first. Loading elements won’t prevent users from abandoning websites with poor performance and high loading times. Loading elements should be used as a last resort when waiting is unavoidable and when loading delay is not caused by unaddressed performance issues.

Using skeleton loaders properly

Skeleton loaders shouldn’t be treated as a replacement for full-screen loading elements but instead when specific conditions for content and layout have been met. Let’s take this step-by-step and see how to use loading UI components effectively and how to know when to go with skeleton loaders instead of regular spinners.

Is loading delay avoidable?

The best way to approach loading in terms of UX is to avoid it altogether. We need to make sure that loading delay is unavoidable and is not the result of the aforementioned performance issues that can be fixed. The main priority should always be performance improvements and reducing the time needed to fetch and display the content.

Is loading initiated by the user and is the feedback required?

In some cases, user actions might initiate additional content to load. Some examples include lazy-loading content (e.g. images) in the user’s viewport while scrolling, loading content on a button click, etc. We need to include a loading element for cases where a user needs to get some kind of feedback for their actions that have initiated the loading process.

As seen in the following mockup, without a loading element to provide feedback, a user doesn’t know that their actions have initiated any loading process that is happening in the background.

Is the layout consistent and predictable?

If we’ve decided to go with a loader element, we now need to choose what type of loader element best fits our use-case. Skeleton loaders are most effective in cases when we can predict the type and layout of the content that is being loaded in. If the skeleton loader layout doesn’t accurately represent the loaded content’s layout to some degree, the sudden change may cause layout shift and leave the user confused and disoriented. Use skeleton loaders for elements with predictable content for consistent layouts.

Is there content on the page that is immediately available to the user?

Skeleton loaders are most effective when there are sections or page elements already present on the page while the skeleton loader is active and additional content is actively loading. Gradually loading in content means that static content is available on page load and asynchronously-loaded content is displayed as it becomes available (for example, the first text is loaded and images after that). This approach ensures that the user maintains a sense of progression and is expecting the content to finish loading at any moment. Having the entire screen covered in skeleton loaders without any content present and without gradual content loading is not significantly better than having the screen covered by a full-page spinner or progress bar.

Creating robust skeleton loaders

Now that we know when to use skeleton loaders and how to use them properly, we can finally do some coding! But first, let me tell you how we are going to approach this.

Most skeleton loading examples from around the web are, in my opinion, over-engineered and high-maintenance. You might have seen one of those examples where skeleton screens are created as a separate UI component with separate CSS styles or created with elaborate use of CSS gradients to simulate the final layout. Creating and maintaining a separate skeleton loader or skeleton styles for each UI component can become serious overhead in development with such a highly-specific approach. This is especially true when we look at scalability, as any change to the existing layout also involves updating the skeleton layout or styles.

Let’s try and find a bare-bones approach to implementing skeleton loading that should work for most use-cases and will be easy to implement, reuse and maintain!

Card grid component

We’ll use regular HTML, CSS, and JavaScript for implementation, but the overall approach can be adapted to work with most tech stacks and frameworks.

We are going to create a simple grid of six card elements (three in each row) as an example, and simulate asynchronous content loading with a button click.

We’ll use the following markup for each card. Notice that we are setting width and height on our images and using a 1px transparent image as a placeholder. This will ensure that the image skeleton loader is visible until the image has been loaded.

<div class="card">
  <img width="200" height="200" class="card-image" src="..." />
  <h3 class="card-title"></h3>
  <p class="card-description"></p>
  <button class="card-button">Card button</button>
</div>

Here is our card grid example with some layout and presentation styles applied to it. Content nodes are added or removed from the DOM depending on the loading state using JavaScript to simulate asynchronous loading.

Skeleton loader styles

Developers usually implement skeleton loaders by creating replacement skeleton components (with dedicated skeleton CSS classes) or by recreating entire layouts with CSS gradients. Those approaches are inflexible and not reusable at all since individual skeleton loaders are tailor-made for each layout. Considering that layout styles (spacings, grid, inline, block and flex elements, etc.) are already present from the main component (card) styles, skeleton loaders just need to replace the content, not the entire component!

With that in mind, let’s create skeleton loader styles that become active only when a parent class is set and use CSS properties that only affect the presentation and content. Notice that these styles are independent from the layout and content of the element they’re being applied to, which should make them highly reusable.

.loading .loading-item {
  background: #949494 !important; /* Customizable skeleton loader color */
  color: rgba(0, 0, 0, 0) !important;
  border-color: rgba(0, 0, 0, 0) !important;
  user-select: none;
  cursor: wait;
}

.loading .loading-item * {
  visibility: hidden !important;
}

.loading .loading-item:empty::after,
.loading .loading-item *:empty::after {
  content: "\00a0";
}

Base parent class .loading is used to activate the skeleton loading styles. The .loading-item class is used to override element’s presentational styles to display a skeleton element. This also ensures that the layout and dimensions of the element are preserved and inherited by the skeleton. Additionally, .loading-item makes sure that all child elements are hidden and have at least an empty space character (\00a0) inside it so that element is displayed and its layout is rendered.

Let’s add skeleton loader CSS classes to our markup. Notice how no additional HTML elements have been added, we are only applying additional CSS classes.

<div class="card loading">
  <img width="200" height="200" class="card-image loading-item" src="..." />
  <h3 class="card-title loading-item"></h3>
  <p class="card-description loading-item"></p>
  <button class="card-button loading-item">Card button</button>
</div>

Once the content has loaded, we only need to remove loading CSS class from the parent component to hide the skeleton loader styles.

These few lines should work for most, if not all, use cases depending on your custom CSS since these skeleton loaders inherit the layout from the main (content) styles and create a solid box that replaces the content by filling out the empty space left in the layout. We’re also applying these classes to non-empty elements (button with text) and replacing it with a skeleton. A button might have the text content ready from the start, but it might be missing additional data that is required for it to function correctly, so we should also hide it while that data is loaded in.

This approach can also adapt to most changes in the layout and markup. For example, if we were to remove the description part of the card or decide to move the title above the image, we wouldn’t need to make any changes to the skeleton styles, since skeleton responds to all changes in the markup.

Additional skeleton loading override styles can be applied to a specific element simply by using the .loading .target-element selector.

.loading .button,
.loading .link {
  pointer-events: none;
}

Multi-line content and layout shifts

As you can see, the previous example works great with cards and the grid layout we’re using, but notice that the page content slightly jumps the moment it is loaded. This is called a layout shift. Our .card-description component has a fixed height with three lines of text, but the skeleton placeholder spans only one line of text. When the extra content is loaded, the container dimensions change and the overall layout is shifted as a result. Layout shift is not bad in this particular case, but might confuse and disorient the user in more severe cases.

This can be easily fixed directly in the placeholder element. Placeholder content is going to get replaced by the content that is being loaded anyway, so we can add anything we need inside it. So, let’s add a few <br /> elements to simulate multiple lines of text.

<div class="card loading">
  <img width="200" height="200" class="card-image loading-item" src="..." />
  <h3 class="card-title loading-item"></h3>
  <p class="card-description loading-item"><br/><br/><br/></p>
  <button class="card-button loading-item">Card button</button>
</div>

We’re using basic HTML to shape the skeleton and change the number of lines inside it. Other examples on the web might achieve this using CSS padding or some other way, but this introduces overhead in the code. After all, content can span any number of lines and we would want to cover all those cases.

As an added benefit of using <br /> elements, they inherit the CSS properties that affect the content dimensions (e.g. the line height, font size, etc.). Similarly, &nbsp characters can be used to add additional spacing to the inline placeholder elements.

With a few lines of CSS, we’ve managed to create versatile and extensible skeleton loader styles that can be applied to a wide range of UI components. We’ve also managed to come up with a simple way of vertically extending the skeleton boxes to simulate content that spans multiple lines of text.

To further showcase how versatile this skeleton loader CSS snippet is, I’ve created a simple example where I’ve added the snippet to a page using Bootstrap CSS framework without any additional changes or overrides. Please note that in this example no text content will be displayed or simulated, but it will work as in previous examples. This is just to showcase how styles can be easily integrated with other CSS systems.

Here is an additional example to showcase how these styles can be applied to various elements, including input, label and a elements.

Accessibility requirements

We should also take accessibility (a11y) requirements into account and make sure that the content is accessible to all users. Skeleton loaders without a11y features might disorientate and confuse users that have visual disabilities or browse the web using screen readers.

Contrast

You might have noticed that the skeleton loaders in our example have a high contrast and they look more prominent compared to the common low-contrast skeleton loaders in the wild. Some users might experience difficulties perceiving and using low-contrast UI components. That is why Web Content Accessibility Guidelines (WCAG) specify a 3:1 minimum contrast for non-text UI components.

The upcoming “Media queries level 5” draft contains a prefers-contrast media query that will enable us to detect user contrast preferences. This will give us more flexibility by allowing us to assign a high-contrast background color to skeleton loaders for users that request a high-contrast version, and have a subtle low-contrast background color for others. I would suggest implementing high-contrast skeleton loaders by default until the prefers-contrast media query becomes more widely supported.

/* NOTE: as of the time of writing this article, this feature is not supported in browsers, so this code won't work */

.loading .loading-item {
/* Default skeleton loader styles */
}

@media (prefers-contrast: high) {
  .loading .loading-item {
    /* High-contrast skeleton loader styles */
  }
}

Animations

Depending on the design and the implementation of animated skeleton loaders, users suffering from visual disorders might feel overwhelmed by the animations and find the site unusable. It’s always a good idea to prevent animations from firing for users that prefer reduced motion. This media query is widely-supported in modern browsers and can be used without any caveats.

.loading .loading-item {
  animation-name: skeleton;
  background: /* animated gradient background */;
}

@media (prefers-reduced-motion) {
  .loading .loading-item {
    animation: none !important;
    background: /* solid color */;
  }
}

Screen readers

To better support screen readers, we need to update our HTML with ARIA (Accessible Rich Internet Applications) markup. This markup won’t affect our content or presentation, but it will allow users using screen readers to better understand and navigate around our website content, including our skeleton loaders.

Adrian Roselli has very detailed research on the topic of accessible skeleton loaders for cases when skeleton loaders are implemented as separate UI components. For our example, I’ll use the aria-hidden attribute in combination with visually hidden text to give screen readers a hint that content is in the process of loading. Screen readers will ignore the content with aria-hidden="true", but they’ll use the visually-hidden element to indicate the loading state to the user.

Let’s update our cards with the ARIA markup and loading indicator element.

<div class="card loading">
  <span aria-hidden="false" class="visually-hidden loading-text">Loading... Please wait.</span>
  <img width="200" height="200" class="card-image loading-item" aria-hidden="true" src="..." />
  <h3 class="card-title loading-item" aria-hidden="true"></h3>
  <p class="card-description loading-item" aria-hidden="true"><br/><br/><br/></p>
  <button class="card-button loading-item" aria-hidden="true">Card button</button>
</div>

We also could have applied aria-hidden to the grid container element and add a single visually hidden element before the container markup, but I wanted to keep the markup examples focused on a single card element rather than on the full grid, so I went with this version.

When the content has finished loading and is displayed in the DOM, we need to toggle aria-hidden to false for content containers and toggle aria-hidden to true on a visually hidden loading text indicator.

Here’s the finished example

That’s a wrap

Implementing skeleton loaders requires a slightly different approach than implementing regular loading elements, like spinners. I’ve seen numerous examples around the web that implement skeleton loaders in a way that severely limits their reusability. These over-engineered solutions usually involve creating separate skeleton loader UI components with dedicated (narrow-scope) skeleton CSS markup or recreating the layout with CSS gradients and magic numbers. We’ve seen that only the content needs to be replaced with the skeleton loaders, and not the entire component.

We’ve managed to create simple, versatile, and reusable skeleton loaders that inherit the layout from the default styles and replace the content inside the empty containers with solid boxes. With just two CSS classes, these skeleton loaders can easily be added to virtually any HTML element and extended, if needed. We’ve also made sure that this solution is accessible and doesn’t bloat the markup with additional HTML elements or duplicated UI components.

Thank you for taking the time to read this article. Let me know your thoughts on this approach and let me know how did you approach creating skeleton loaders in your projects.

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The post A Bare-Bones Approach to Versatile and Reusable Skeleton Loaders appeared first on CSS-Tricks.

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This content originally appeared on CSS-Tricks and was authored by Adrian Bece