Slow scripts and animating expensive CSS properties can result in jank as the browser struggles to hit a smooth frame rate. For a rate of 60 frames per second, the browser has 16.7 milliseconds to execute scripts, recalculate styles and layout if needed, and repaint the area being updated. It's commonly accepted that 60 frames per second is the rate at which animations will appear smooth. However, the performance cost of modifying a CSS property can vary from one property to another. They can also give better performance, as they give the browser more control over when to render frames, and to drop frames if necessary. The browser creates the animation as a transition from each keyframe to the next.Ĭompared with animating elements using JavaScript, CSS animations can be easier to create. With CSS animations you specify a number of keyframes, each of which uses CSS to define the appearance of the element at a particular stage of the animation. Using these tools you can measure an application's animation frame rate, and diagnose performance bottlenecks if any are found. The developer tool's frame rate and waterfall charts provide insight into the work the browser is performing to animate code. We'll also discuss some tips to create and maintain a fast and steady frame rate. Let's take a look at how we can use browser tools to inspect the frame rate. While it is not always possible to maintain 60fps, it is important to maintain a high and steady frame rate for all animations. Responsive user interfaces have a frame rate of 60 frames per second (fps). Animation can help make a site feel faster and responsive, but animations can also make a site feel slower and janky if not done correctly. Users expect all interface interactions to be smooth and all user interfaces to be responsive. While performance is sensitive to the particular system and its load, performance tools can help you understand the work the browser's doing to render your site, and help you prevent and diagnose problems when they occur. These animations can consume CPU and/or cause jank. Code based animations, be it CSS, SVG,, webGL or other JavaScript animations, can cause performance issues even if the bandwidth footprint is small. The performance cost of animating a CSS property can vary from one property to another, and animating expensive CSS properties can result in jank as the browser struggles to hit a smooth frame rate.įor animated media, such as video and animated gifs, the main performance concern is file size - downloading the file size fast enough to not negatively impact performance is the greatest issue. Animation on the web can be done via SVG, JavaScript, including and WebGL, CSS animation,, animated gifs and even animated PNGs and other image types.

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