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Comment by runawaybottle | Hacker News Reader

What does Preact sacrifice to get down to 3kb? Browser support? Nothing comes for free I guess, so just curious about the too good to be true nature of it.

Why isn’t the React team putting in these enhancements?

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They don't do the event normalization/redirection. This is something you probably won't notice or need in your project anyways. I myself encountered the difference just once, when using Portals: In React, all events inside the portal would bubble/propagate to the parent components of the React component tree just as if the portal was mounted as a child of the surrounding component. In preact, all events in the portal propagate to the actual, real browser DOM hierarchy. I.e. if you have a click event inside the portal, the wrapping Preact parent component would never see the event or be able to handle this. This incompatibility would only be an issue when migrating to Preact from React; if you start with Preact from the beginning you would refrain from using this event bubbling to notify the enclosing component and use some other mechanism (i.e. forward the event data through a custom event handler or PubSub instance).

Synthetic event system + render decoupling. Preact uses the event system of the platform (browser) and only renders to it (there's no react native support).

Anyway we are using it at prod and allowed us to reduce our bundle sizes ;)

Worth noting that while Preact specifically doesn’t support React Native, JSX does. So to the extent the dev APIs stay in line you can always swap out the underlying library for that target (or other renderers).

They have most of it listed in their docs here: https://preactjs.com/guide/v10/differences-to-react/

There are a few stuff that are missing from core preact that can be added via preact/compat package namely: memo, forwardRef, PureComponent, Event listener modifications similar to react, etc.,

They sacrifice all the crazy performance optimisations that React has.

TBH preact is faster than React. I don't know of a scenario where react was faster.

How do you measure? I’d love to see large renders and complex top level state updates that hit hundreds of components.

This is relevant, though it is 2 years old: https://medium.com/@ajmeyghani/javascript-frameworks-perform...

I worked on a project where we were using React 14 before 2 years. It was only a desktop B2B site and later on when mobile support was inevitable we tried to use preact for mobile site since it was lightweight. We actually found that our desktop site which renders large tables with hundreds of rows and multiple chart components performed better in Preact without any optimizations. I'd say maybe a 20 - 30% improvement since we were seeing a gain FPS of around 10 frames. I think it would have been a bit more faster if we had used MobX instead of redux but that was too late.

Haven’t worked with React for a little while and only ever used MobX on one project, I was mostly using Redux. What performance improvements does MobX offer?

Redux always returns a brand new state. This will cause all consumers to rerender and react will update the dom only if there is a change. But with Mobx its more granular and the updates are atomic. This isn't a problem in apps where there is a single team working on it. But when you work in enterprise apps where different parts are worked on by different teams state updates to redux can be costly. This is not a limitation of Redux but a human problem that occurs inevitably. I've seen this in 3 different large scale projects. It starts well but after a year or so when people move out/in this bites us.

This can be enforced with strict rules, eslint plugins and infra but they are expensive as hell.

EDIT: 'This will cause all consumers (with incorrect mapStateToProps configuration) to rerender'

Understood, this is the reason I suspected and have spent considerable time in the past optimising state updates to forms in React and Redux projects so can imagine how this would become an issue in much larger teams than the ones I was working in.

When using Redux, components are supposed to select small parts of the state tree, and then they only rerender when those change. It is absolutely not the case that all components render on each unrelated update of the global state, that would be crazy.

https://react-redux.js.org/next/api/hooks#useselector

It is true that all of the selector functions need to run on each change, but those are supposed to be really small pure functions and their performance should be negligible, compared with everything else that normally happens in an app.

Edit: It is absolutely possible to affect performance with Redux, especially on a large app — for example if hundreds of selectors need to run for every keystroke in a textbox.

Yeah this is correct, I think what the OP was getting at was the fact that Redux requires a little more discipline as it's less opinionated than MobX.

Yes you are correct that we can use useSelector to optimize selectors for Redux and I even implemented this hook in an interview on the whiteboard :D.

And yeah components are supposed to select only what they need in mapStateToProps and mapDispatchToProps. But I have seen a couple of instances where this is not followed and the developer chooses to use the entire state object passed to the component. This was fixed quickly and all developers got a short doc on the do's and dont's of Redux. This is what I mean by the extra work around redux library and not the concept itself.

Also its a fairly common to see developers pushing multiple micro updates like keystrokes to redux making it slow down. This gets filtered in the reviews but it misses out sometimes. I'm guessing this to happen in many other projects too unless I'm missing out on some major update on the tooling around redux.

These problems are not because of the approach but in the implementations. I hope you get what I mean by cost in my opinion above.

Agreed then, Redux does give you enough rope to get into trouble, especially when used indiscriminately.

You still have to run the selectors for all components on each change and check if their result has changed and if so, update the component props. So the more components, the more memory/cpu you waste on each redux update. So now you have to use something like reselect to start caching results...

Also it'so easy to start making new components dependent on the store, and ending with reusability.

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