What is a “task”? When it comes to normal Javascript, it’s everything that we put in the script tag and execute synchronously. And continue, non-stop, working tirelessly so that we are able to do such important things as doom-scrolling on Twitter without even noticing the effort it took.
If it has more time, it executes the next task, and so on, until no more time is left in that ~13ms gap, and then refreshes the screen. The browser grabs a task from the queue and executes it. The information that updates those slides is split into “tasks”. This is what we refer to as “painting” in React. One slide changes to the next one ~every 13 milliseconds. Normally, modern browsers try to maintain a 60 FPS rate, 60 frames per second.
#4 elements ii flickering how to#
If a very slow browser was asked to come up with an instruction on how to draw an owl, it could literally be the infamous picture: Instead, it’s more like showing slides to people: you show one slide, wait for them to comprehend the genius idea on it, then transition to the next slide, and so on. It’s not like drawing on a whiteboard, where you draw lines, erase lines, write some text or sketch an owl.
#4 elements ii flickering update#
Browsers don’t continuously update everything that needs to be shown on the screen in real time. In React world it is also known as “painting” just to differentiate it from React’s rendering - those are very different! The idea here is relatively straightforward. The first thing we need here is “browser rendering”. Why the fix works: rendering, painting and browsers To answer those questions, we need to step aside from React for a moment and talk about browsers and good old Javascript instead. But what exactly does this mean from a practical sense? Do I need to think about low-level concepts like browser painting when writing simple dropdowns now 🤯? Why is that? It also says that it is fired “before the browser repaints the screen”, which implies that useEffect is fired after. Is it safe to do though? Why don’t we just use it everywhere instead of useEffect? The docs explicitly say that useLayoutEffect can hurt performance and should be avoided. This is pure magic, no more initial flashing, check it out: In React version from ~16.8 (the one with the hooks) however, all that we need to do is replace our useEffect hook with useLayoutEffect. This is how we used to handle cases like this in the past. And only after we extract the dimensions and the magic number, make them visible. So one possible fix for this would be to still render that first pass, but invisibly: with opacity set to 0, or in some div somewhere outside of the visible area. And we have to render them first, otherwise, fancy responsiveness won’t work. The reason for that flash should be pretty obvious: we render those items and make them visible before removing unnecessary items. We definitely need to fix it before it goes into production. You should be able to clearly see that initial render - when all the items in the menu and the “more” button are visible. Unfortunately, there is a horrible flash of content there. Try to refresh it a few times, especially with slowed down CPU. Only don’t get too excited just yet: there is one major flaw in the user experience here.
#4 elements ii flickering full#
For a “proper” responsive experience we also would need to listen for the resize event and re-calculate the number, but I’ll leave it up to you to implement.Ĭheck out the full working example in the codesandbox below. That’s about it! Now, after state is updated with the actual number, it will trigger a re-render of the navigation, and React will re-render items and remove those that are not visible. It’s going to be just a component that accepts an array of data and renders proper links: It can render a row of links and can adjust the number of those links based on the container size.Īnd if some links don’t fit, show a “more” button that will open them in a dropdown menu if clicked. It’s coding time! Let’s do something fancy today: a responsive navigation component. In the process, we’ll find out everything that we need to know about useLayoutEffect, when and why we’d want to use it instead of useEffect, how browsers render our React code, what is painting, why all of this matters and how SSR plays a role here. So, what is the problem with it, exactly, and why are "normal" tactics not good enough? Let’s do some coding and figure it out. There is, however, another very important, although quite rare, topic when it comes to dealing with DOM: changing elements based on real DOM measurements like the size or position of an element. In the previous article (Refs in React: from access to DOM to imperative API) we covered how to do it with Ref, and learned everything about Ref as a bonus. Let’s talk a bit more about DOM access in React.
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