![]() ![]() Creates a bad user experience, as a result of all the above.May increases First Contentful Paint (FCP) times.Layout thrashing or forced reflow can be the cause of bad user experience, in terms of elements shifting around while the user tries to read or interact with the page or by reducing our site’s frame rate resulting in a janky "webby" feel. This will fix the layout avalanche effect and result in no layout whatsoever by the browser as shown below: Avalanche effect fixed Why it is bad # In this CSS grid of list items for example, let's say that I change the width and height of each item on hover: Hovering over one image can cause layout and layout shift, but it could end up into a layout avalanche effect when the rest 19 images in the page are "pushed" left and right due to the first image's new position and/or dimensions. Say for example, we are rendering a long list of 20 image-links in a page that change styles on hover. In some cases, we have to be extremely careful on the front-end when it comes to rendering or adding interactions to a number of list items. The layout avalanche effect # Warning: Flashing images follow! When it happens #įor a detailed list, check out this list of CSS properties that trigger layout, painting, and composition and this list of JavaScript tasks that trigger layout. So what exactly is this Layout thingy? Simply put, layout is a synchronous and main thread blocking operation that computes dimensions and positions for all elements in a document. and 3.) have a look at the Cumulative Layout Shift (CLS) and Optimise Cumulative Layout Shift articles to learn more about it. If you would like to learn more about how to improve Unwelcome layout shifts ( 2. ![]() In this article we will be focusing mostly on these. It is important here to note that even though Layout ( 1.) is essential for laying out all elements in the screen, when requested multiple times from the browser synchronously, it can be detrimental to runtime performance ( 4.). Layout thrashing or uninterruptible reflow or forced reflow: A series of layout or reflow ( 1.) events usually resulting in slow frame rendering times (low FPS).results in a noticeable shift of elements within the viewport Layout or reflow: It's the act of figuring out the rects for everything (or a subset) in the document.In order to simplify things and give some clarity around the different browser processes and names, let us go through them and make sure we are referring to the correct items throughout this article: What is Layout, reflow, Layout thrashing and Layout Shift? # I will also assume you have a basic understanding of Chrome DevTools as we will be diving in deeper later on. Prerequisites #įor the rest of this article, I will assume you are comfortable with front-end development components such as CSS, the Browser DOM, and accessing HTML elements using JavaScript. We will also be looking at how we can use advanced tools within Chrome DevTools to locate and analyse performance bottlenecks. We will be diving into various ways that we can optimise a site and reach 60 frames per second (FPS) - 16 ms per frame - or even 90 and 120 FPS for newest mobile phones, while the user interacts with or loads a page. In this article, we will be looking at a few ways by which Layout / reflow events might occur, why they are bad, how to track such events and how to optimise for blazing fast frame rate on the web. In the modern web, having a Progressive Web App (PWA) that a user can launch from the homescreen, it is expected that the web app is fast and has a 60 frames-per-second (FPS) smoothness without feeling janky. An experience is often characterised as " webby" when it feels janky during scroll, animations or transitions. ![]()
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