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Optimizing React Rendering
- mercer 9y agoThis is actually a pretty decent article, in part because it signals its audience properly: (semi-?)experienced React developers who haven't dealt with optimization yet.
- bobsam 9y agoso basically the Facebook app team? Edit: sorry guys, didn't knew you were all on HN :(
- devopsproject 9y agoThe downvotes are sad. Are people this far gone that they can't take a little criticism?
- e1g 9y agoOfftopic, but regarding the downvotes - I have been using FB front-end projects for several years, and today I see them as _the_ gold standard for a supportive, mature, well-governed, and consistent FoSS ecosystem. I struggle to recall any snarkiness, cynicism, or even rudeness. I'm sure it happens, but I closely monitor several of their projects and the behavior is mostly exemplary even without considering the size of the user-base. Besides near-exemplary FoSS behavior, FB engineers must solve problems well beyond what most industry will ever attempt, and then present some of their solutions on a silver platter for the rest of us. Of course, it's not perfect, and sometimes confusing, and sometimes over-engineering, but I would personally pay $xx,000 per year to use any library of the same standard as they give out for free. So when I see a callous comment that takes nothing to write and could cause someone to feel degraded about their vast contributions, I downvote. It's not about safe places, it's about professional respect and courtesy.
- bobsam 9y agoSeriously? HN has really short memory... https://news.ycombinator.com/item?id=11057857 https://news.ycombinator.com/item?id=11057857 https://news.ycombinator.com/item?id=10066338 https://news.ycombinator.com/item?id=10066338 https://news.ycombinator.com/item?id=14082491 https://news.ycombinator.com/item?id=14082491
- seattle_spring 9y agoWhat's the real criticism in his or her post? I see nothing other than a completely unsubstantiated accusation.
- devopsproject 9y agoseems like the complaint is facebook=slow. Would you say that facebook is a good example of a fast site\app?
- seattle_spring 9y agoAnyone else sick of the incredibly lazy "shill"-type accusations being thrown around lately? Just because a post is heavily upvoted or downvoted does not mean the team behind the post is brigading or manipulating it. Let's loosen those tinfoil hats just a bit.
- bobsam 9y agoThis was all said on jest, chill man! But now that we are at it, why don't you give me another probable reason a harmless comment was downvoted?
- pawelwentpawel 9y agoQuick question - can printWasted be used with RN too?
- dounan 9y agoHaven't tried this myself, but this might be what you're looking for: https://github.com/facebook/react-native/issues/9146#issuecomment-277434523 https://github.com/facebook/react-native/issues/9146#issueco...
- pawelwentpawel 9y agoThanks! I'll give it a go.
- metalliqaz 9y agoFrom the article: > Fixing the issue is pretty simple*. We simply need to short circuit the re-rendering for a subtree if we know that the subtree hasn’t changed. Not a frontend guy but I've seen this theme more than once on HN recently. It seems to me that addressing this anti-pattern would be built right in to modern React components. Isn't efficient DOM manipulation by pruning non-necessary changes kind of their thing?
- msoad 9y agoReact won't update the DOM when render returns the same result but if you can avoid those unnecessary render calls you save some scripting time. Front-end developers have to be very conservative when it comes to running JS code. Welcome to single threaded everything programming!
- wcjordan 9y agoIt is, so a DOM change wouldn't occur, but in these cases you still go through a React rendering to virtual DOM phase (templating) and the DOM tree reconciliation. Since these can be slow (although much faster than a DOM change), it makes sense to check and skip those steps when you can. The focus of most of this article is how you can skip those steps when you're components input data is unchanged and common gotchas related to that. Some other great posts in this vein are: https://facebook.github.io/react/docs/optimizing-performance.html https://facebook.github.io/react/docs/optimizing-performance... and http://benchling.engineering/performance-engineering-with-react/ http://benchling.engineering/performance-engineering-with-re...
- robto 9y agoI think it is an anti-pattern that is a result of the language it's built on. This is one place where using Clojurescript wrappers of React has a real payoff - immutable datastructures make equality checking very very cheap.
- doctorcroc 9y agoA good patch for this is ImmutableJS
- positivecomment 9y agoIs there special logic in react that binds arguments of a function to the props with the same name? I'm talking about the handleDelete "fix" in the article: render() { const views = this .props.dataList.map((d, i) => { return <Data data={d} index={i} onDelete={this.handleDelete} /> }); } handleDelete(index) { //... } I guess they just call that function from within the Data component with the correct parameter. But then, Data component needs to know how to call that function. Is there a better way?
- deleted 9y ago[deleted]
- kentor 9y agoNope. For dom elemenets I have been using `data-{name}` attributes, and pulling them out from the handler using `e.currentTarget.dataset.{name}`
- nip 9y agoBy using the property initializer syntax [1] [2] [1] https://facebook.github.io/react/docs/handling-events.html https://facebook.github.io/react/docs/handling-events.html [2] https://babeljs.io/docs/plugins/transform-class-properties/ https://babeljs.io/docs/plugins/transform-class-properties/
- Silhouette 9y agoThat solves the problem of binding 'this', but doesn't solve the problem of supplying the index to the callback function. Essentially you have only two options for doing that. One is to bind the callback function to a certain index in advance and then supply that callback to your child via props so it already knows the relevant index and doesn't need calling with any extra parameters. The trouble with this one is that it creates a new function every time, which is inefficient in itself and horrible if it winds up causing your child to rerender because props changed even though in practice you're passing an identical function every time. The other is to supply a callback where the child component is responsible for supplying the extra index information when it calls the function, either by directly passing the index as a parameter or via an indirect route such as using data-* attributes as 'kentor mentioned. This is more efficient, but it creates tighter coupling between the child and parent components. In practice, it seems most projects adopt the second strategy because the tighter coupling is usually much less of a problem in practice than the performance penalty, but neither solution is ideal. Unfortunately, JavaScript's semantics don't make it easy to have the equivalent of a "deep equal" comparison on functions that would return true for two copies of the same function with the same bound values.
- sophiebits 9y ago> So all you have to do is use PureComponent everywhere and you’re good to go. There’s nothing more to it. Enjoy your new blazing fast React app! (I work on React.) This isn't quite right. If we recommended that PureComponent be used everywhere, it would probably be the default already. Rather -- the comparison to decide whether or not a component should be rerendered costs something, and in the case that you do want to rerender, all of the time spent checking whether you should have rerendered is wasted. Instead, we'd suggest you be conscious of where you need to do the comparisons. It's usually only in a couple of places in your app. Good candidates are on the children of a long list or around large parts of the app that change independently (that is, cases where you know the parent should often rerender but the child shouldn't). A few well-placed shouldComponentUpdate (or PureComponent) uses can go a long way.
- diggan 9y agoLiterally the next section is "*Except…", so might want to continue reading the article before leaving your comment here
- spicyj 9y agoHi! I did read the whole article and don't believe it addresses the point that I called out in my comment. I hope you'll agree after reading the article and my comment carefully.
- dmnd 9y agoHi Ben! At the React conference, I asked Sebastian Markbåge (also a React author) why `PureComponent` wasn't the default and he said there were already too many new concepts when React was released, and it would have made adoption harder. But he implied that maybe it should be the default. (Then again, alcohol was involved so I could be misremembering.) When using immutable data structures the comparison in `shouldComponentUpdate` is very cheap. Assuming that, using pure components everywhere is very tempting for simplicity. Correct me if I'm wrong, but React creates an object for every component to pass props around. Constructing that object is linear in the number of props. An additional `shouldComponentUpdate` check for each component is also linear in the number of props. So using pure components everywhere is at worst adjusting the constant. Also, in a world where PureComponent is the default, perhaps React could monitor the "hit rate" of `shouldComponentUpdate` and decide to not call it if a component returns true too often?
- drinchev 9y agoI would generally say that there is a reciprocal relationship of performance and maintainable code, no matter what you use. React is a powerful way to build your front-end, but it's power is in structure / code. In my experience with React, fine-tuning components for faster rendering is always a pain. Too much magic happens behind the scenes and too difficult to keep that in mind while writing your beautiful components.
- pvg 9y agothere is a reciprocal relationship of performance and maintainable code There isn't an inherent one, it's just that writing for both is much harder than just for one.
- CCing 9y agoOff-topic: what is the theme and color syntax theme ?
- dounan 9y agoAtom editor with the 'One Dark' theme
- acemarke 9y agoPretty good post, minus the advice to always use PureComponent everywhere (per Ben's comment in this thread). If anyone's interested, my React/Redux links list has a large section of other articles on various React-related performance concerns, including benchmarking and optimization approaches: https://github.com/markerikson/react-redux-links/blob/master/react-performance.md https://github.com/markerikson/react-redux-links/blob/master... .
- wbc 9y agoWould using mobx to manage state solve most of these problems?
- aidos 9y agoYeah. That's exactly what I was thinking as I read through the list of gotchas. We've just started using mobx ourselves. There's still a weird contention between events and state that I'm yet develop patterns for but overall I'm really happy with it.
- mendelk 9y agoAlong the same lines as the advice in TFA: If you pass an object literal as the `style` prop, it'll always re-render, because the object reference will change. Solution: instead of the object literal, pass a reference to an existing object.
- uranian 9y agoFor some reason the focus is always on preventing re-rendering if it comes to optimising a React app. I understand that it can be really effective and is often the easy way out, but re-rendering in itself is not costly and I don't really care about it the most of the time. I am more concerned that the code that runs during a re-render is not rebuilding huge static lists that never change and so. I see that over and over again in React apps. I tend to build a lot of the static stuff in the ComponentWillMount stage to prevent that. Only when already optimised code is getting to slow I start thinking about preventing re-rendering if possible. My reason for not starting with ShouldComponentUpdate is that you have to be very careful not creating nasty bugs with that like I did some times. If a year later you write some code and it doesn't work for some reason it is painful if you find out after a long search that a stupid child component did not update for some prevention rule you forgot about. I really try hard to avoid premature optimisations.
- dounan 9y agoThat's a great point, and being aware of the dangers of shouldComponentUpdate is what this post is all about. There are a lot of gotchas when using PureComponents, and can lead to bugs if you're not careful. Also, recalculating derived data (building static lists) in render() is very wasteful, and is also another gotcha when using PureComponents (object copying). Removing object copying from render() speeds up the actual render() call and allows you to take full advantage of PureComponents. We are experimenting with ways to make all of this a bit easier, and hopefully will have some good news to share in Part 2 :)
- ChrisCinelli 9y agoOne thing that has been bothering me is that React is slow by default. It re-renders everything every time unless you start looking into shouldComponentUpdate. Even if I agree that premature optimization is the root of all evils, I like when the language and the framework I use make it writing fast code as easy as writing slow code. I wonder if anybody has evaluated, the improvement they get in development speed using React when they add the time they have to spend to optimizing their React code. In my experience, I am not even frustrated with React itself most of the time but with the other things in the ecosystem.
- dounan 9y agoIn our experience, React is not necessarily 'slow' by default. Re-constructing parts of the element tree each time can be a bit wasteful, but it is only as slow as your render() methods, and that is outside of React's control. We have survived over 3 years with a massive application (over 2000 modules) and tons of wasteful re-rendering, but have only now started to notice any sluggishness. That makes React pretty fast in my mind. Having said all that, we are experimenting with an 'all PureComponents' approach to potentially make React, but whether that turns out to be a good idea is yet to be seen (object comparisons in sCU are not free).
- seangrogg 9y agoHmm, my experience has been pretty much the opposite. Even without optimization, React's renders won't cause a DOM update unless there is something to diff - I can't say the same for jQuery or Angular 1.x. As well, being big on the "don't use it unless you need it" bandwagon I tend to wait until I see components and re-use in my code before I import React in the first place. If the total re-render is occurring under 16.67ms (60fps) in a non-trivial use-case I'm usually fine leaving it as-is. Most render cycles taking longer than that involve operations on large data sets or events firing at the millisecond level (mouseover, drag, etc) - and those are worth fixing as they'll actually have noticeable impacts on the user experience. But I tend not to optimize just to pat myself on the back for "optimization".
- mstijak 9y agoI'm the author of CxJS[1] which uses React for rendering. Before rendering, the whole tree is scanned for data changes and with that information available shouldComponentUpdate is very simple. Another technique that I find very useful is to use a dedicated data declaration component which then decides if children should update or not. Try grid sorting on this page: https://worldoscope.cxjs.io/yyrsmjk https://worldoscope.cxjs.io/yyrsmjk [1]: https://cxjs.io https://cxjs.io
- joncampbelldev 9y agoFrom what I've found in my current job creating a js react app as well as side project with cljs is that advanced optimsation of js react === basic usage of clojurescript reagent. I've found no redeeming features when developing the is app, issues with hot reloading and constant integration work to get everything to play nice with immutable js
- joncampbelldev 9y ago*the js app