Mastering the will-change CSS Property: Optimize Your Web Animations and Filters

The will-change CSS property is a powerful but often underutilized tool in web development. By giving the browser hints about upcoming changes, will-change can improve the performance of animations and transitions, especially when working with complex filters or transformations.

In this in-depth guide, we’ll explore the will-change property, its benefits, use cases, and potential pitfalls. Through practical examples, we’ll teach web developers, software engineers, and design enthusiasts how to optimize their web applications effectively.

What is the will-change Property?

The will-change property allows developers to inform the browser about the types of changes an element is expected to undergo. This advance notice enables the browser to make optimizations, such as promoting an element to a new rendering layer, which can significantly enhance performance during animations or dynamic transformations.

Syntax

.element {
  will-change: <property>;
}

• property: Specifies the property or properties that are expected to change, such as transform, opacity, or filter.

Commonly Used Values

• transform

• opacity

• filter

• scroll-position

Why Use will-change?

Modern browsers perform numerous optimizations to ensure smooth animations and transitions. However, some changes require recalculations that can introduce jank or reduce frame rates.

Benefits of will-change:

• Smooth Animations: Prepares elements for transformations or opacity changes, preventing frame drops.

• Improved Filter Performance: Enhances rendering of complex filters like blur() or brightness().

• Efficient GPU Utilization: Moves elements to their own rendering layers, reducing the workload on the main thread.

Caveat: Use Sparingly

Overusing will-change can negatively impact performance by increasing memory usage and GPU overhead. Apply it only when necessary and remove it once changes are complete.

Practical Examples

Example 1: Enhancing a Filter Animation with will-change

Consider a button with a hover effect that applies a blur filter. Without will-change, the browser may lag as it recalculates the rendering on hover.

HTML and CSS Without will-change

<button class="blur-button">Hover Me</button>

<style>
  .blur-button {
    padding: 10px 20px;
    font-size: 16px;
    transition: filter 0.3s ease;
  }

  .blur-button:hover {
    filter: blur(4px);
  }
</style>

Adding will-change

<style>
  .blur-button {
    padding: 10px 20px;
    font-size: 16px;
    will-change: filter;
    transition: filter 0.3s ease;
  }

  .blur-button:hover {
    filter: blur(4px);
  }
</style>

Outcome:

With will-change, the browser optimizes the element for filter changes, ensuring smoother transitions.

Example 2: Optimizing Transformations

A card flip animation can benefit from the will-change property for seamless rendering.

HTML and CSS

<div class="card-container">
  <div class="card">
    <div class="front">Front</div>
    <div class="back">Back</div>
  </div>
</div>

<style>
  .card-container {
    perspective: 1000px;
    width: 200px;
    height: 300px;
  }

  .card {
    width: 100%;
    height: 100%;
    position: relative;
    transform-style: preserve-3d;
    transition: transform 0.6s ease;
    will-change: transform;
  }

  .card:hover {
    transform: rotateY(180deg);
  }

  .front, .back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
  }

  .back {
    transform: rotateY(180deg);
    background-color: lightblue;
  }

  .front {
    background-color: lightcoral;
  }
</style>

Outcome:

Adding will-change: transform; ensures the browser optimizes the element for 3D rotations, resulting in a smoother flip animation.

Example 3: Dynamic Updates with JavaScript

If you’re applying changes dynamically, you can set will-change via JavaScript just before the change occurs and remove it afterward.

JavaScript Example

<div class="dynamic-box">Dynamic Box</div>

<style>
  .dynamic-box {
    width: 150px;
    height: 150px;
    background-color: coral;
    transition: transform 0.5s ease;
  }
</style>

<script>
  const box = document.querySelector(".dynamic-box");

  box.addEventListener("click", () => {
    // Add will-change just before applying transformation
    box.style.willChange = "transform";

    // Apply transformation
    box.style.transform = "scale(1.2)";

    // Remove will-change after the animation
    setTimeout(() => {
      box.style.willChange = "auto";
    }, 500); // Match the transition duration
  });
</script>

Outcome:

Dynamically applying and removing will-change ensures efficient memory usage.

When (and When Not) to Use will-change

Use will-change When:

• Animating properties like transform, opacity, or filter.

• Handling complex visual effects like box-shadow or clip-path.

• Optimizing elements with frequent repainting or reflow.

Avoid Overusing:

• Avoid applying will-change **globally **or to many elements.

• Do not leave will-change applied indefinitely, as it can cause high memory usage.

Performance Considerations

Browser Support

will-change is supported in all major browsers, including Chrome, Firefox, Safari, and Edge. Check compatibility for older browser versions on MDN Web Docs.

Testing Performance

To measure the impact of will-change, use browser developer tools:

• Open DevTools in Chrome or Firefox.

• Navigate to the Performance tab.

• Record animations or interactions to see frame rates and layer promotions.

Summary: Key Takeaways

The will-change property is a valuable tool for optimizing animations and transitions in web development. By giving the browser hints about expected changes, you can significantly improve performance and user experience.

Pros of will-change:

• Smooth animations and transitions.

• Efficient rendering of filters and transformations.

• Enhanced GPU utilization for complex effects.

Caution:

Use it sparingly and remove it when no longer needed to avoid unnecessary memory usage.

Conclusion

The will-change CSS property is a game-changer for developers aiming to create high-performance web applications. By strategically applying it, you can ensure smooth animations, reduce jank, and deliver a polished user experience.

Start experimenting with will-change in your projects today and see the difference it makes in your web animations and interactions!

Further Reading

• MDN Web Docs: will-change

• CSS Tricks: When to Use will-change