We explored this at a previous company I worked at. The conclusion at the time was that the message passing model was not yet efficient enough at the time because of serialization/deserialization which nullified any performance gains. Transferrable objects at the time were really new. If the support for shared memory has improved, it might now make sense.

The biggest problems with performance are:

- GC pauses

- triggering reflow

- marshalling data across interfaces (serialization/deserialization of native types into strings and back again).

That last one is an absolute killer when it comes to applying 3D matrix transforms. Basically, you're taking an array of floats, serializing them into a string to do an element.style property assignment, so that the browser can then take that stringified representation and convert it back into an array of floats that it can apply. Huge perf hit here.

I haven't found serialization to be anywhere near the bottleneck. How long does it take to serialize/deserialize a 16 element array? I could see how this would be an issue if you had hundreds of them per frame. But for most purposes an entire 16 element array is overkill and you could probably come up with a more compressed description of the transforms (scale, rotate, translate) and consider adding a pooling layer.

People attribute pauses to GC, when it's sometimes just the browser container environment acting up and there's nothing we can do about it - so it's easy to write it off as GC. Not sure about today, but 1.5 years ago (i = new Image(), i.src="http...") could block the JS thread for as much as 19ms. In a larger app, it's easy to write that off as GC, but (at least on iOS) the performance tooling is really lacking and it's tough to find the culprit.

Reflowing is a big deal, I agree.

Basically if you want to prevent reflowing you end up making everything a texture and that leads you to making many many CSS transform changes on every frame. 60fps is easy to hit on a modern desktop, but mobile performance requires more effort to achieve an effect that feels natural. The problem with the marshalling is that it is comparatively expensive and a blocking operation, which is not conducive to buttery smooth graphics performance on all platforms.

Blowing out texture memory accidentally was also a big deal when I was measuring this stuff.

You can now transfer typed array data using the newest postMessage API. http://updates.html5rocks.com/2011/12/Transferable-Objects-L...

Me me! I'll be exploring this soon and I'm sure I'll reach out for help before I get too far. Could do a lot of stuff off thread, from data to layout calcs. My profile should have some info related to the hybrid stuff.

Very cool! I'll keep an eye on your work!

Me too.

I'd love to chat more about this with both of you, this seems like a direction definitely worth exploring.

Maybe we could set up a github project for it? Or talk in an issue on your existing repo, nwienert?

I'd like to see a github repo. You can hit me up on twitter, info in my profile. I think even just finding the right library to make using webworkers + npm + webpack would be great to start, because honestly its all the other stuff that slows down the thread. React can run on the main thread for the most part.

Some reading:

https://news.ycombinator.com/item?id=6982485 http://stackoverflow.com/questions/18056922/is-there-a-way-t...

Edit: webpack + webwoker: https://github.com/webpack/webpack/tree/master/examples/web-...

Cool, I set up a repo and started a wiki on it,

https://github.com/kripken/worker-ui/wiki

Not familiar with webpack, will take a look.

If you're interested in doing it with React, here's a video explaining how to do a custom backend: https://www.youtube.com/watch?v=eNC0mRYGWgc

You basically need to change BackendIDOperations and ReactEventListener to send/receive messages vs talking to the real APIs. It's already set up in the codebase to do this (because it actually worked at one time).

Webpack, per usual, already thought of this and has an answer for you :) https://github.com/webpack/worker-loader

Sweet. I'll watch out for wherever you guys end up.

Might be worth reading one of the react native devs about why animations might still be hard: http://jlongster.com/First-Impressions-using-React-Native#co...

This idea is also why I hooked up the css-layout project (https://github.com/facebook/css-layout) to a live demo to play around with: http://layout.jlongster.com/

Yes, in browsers, JS animations are still hard (I might even say impossible to do well for large apps with a lot going on). One anecdote: I spent a month trying to build a 60fps scrolling list view in JS from scratch (JS driving all the animations). No matter how hard I tried, I couldn't make it work on the web. I believe it was image decoding interfering but it's difficult to say why. Then I took that same example, which by that point was optimized, and ported it to React Native in a few hours(where we have off-thread image decoding and timers I can trust) and the example was like butter.

Now of course, I had hand optimized the performance, but my point is that on the web, there was nothing I could do, and with React Native, there was something I could do to make animations smooth. This is not to say you should be doing animations in JS, but if you want highly customizable interactions that can be immediately stopped by a touch processed in JS, you should try it out and see how it feels. For things that are "fire and forget", or platform specific, you should try using CoreAnimation/keyframes etc which protects the animation from your business logic.

Interestingly, this comment, while probably being of the most technical detail / value in the thread, was downvoted by someone :)

what's wrong with -webkit-overflow-scrolling: touch? doing scrolling in js is so last year.

You can't build the equivalent of UITableView (which is a very important component in almost any iOS app) without frame-by-frame scroll events.

How so? Which feature of the UITableView can not be replicated in JS? I'm struggle to think of one. Swipe left/right to remove rows in a table can be done with touch events.

What am I missing?

I think you're not being specific enough. I am claiming they can perfectly be recreated in JS, just not within a mobile browser at the moment.

I do mean within a mobile browser. We have a pretty large app inside Cordova, and I've yet to get stuck where there's something I can't recreate. Would be interesting to see an example where a mobile browser falls short.

Right, but then you're susceptible to animation stutter and you have to reinvent the look-and-feel of the platform, which is extremely difficult.

Exactly. Customizing exactly how a header bar "sticks" to the top when it hits a certain point, cannot be done with any built in browser scroller. The same is true of any animation that should happen in sync with the scrolling itself (think like a parallax fade/scale animation etc).

What most apps need can be done by listening to touch events instead of scroll events. Eg hiding the top bar when user started scrolling down and so on.

I can't even think of an app that has a parallax effect. If your app is required to have complex animations then web tech is not the right tech choice in general imo

Also worth looking at some ideas we have for doing cross-thread component hierarchies in React:

https://github.com/reactjs/react-future/tree/master/05%20-%2...

oh nice, thanks for mentioning this.

I am not a maintainer and I just tried it briefly so I am not 100% sure of the allegations they make on their front-page, but it seems like http://gridstylesheets.org are using Workers to run their layout algorithm (Cassowary Constraint Solver) and absolute-position elements (using 3D transforms).

EDIT: Searching for "Worker" right now didn't bring any mention, but it seems it is a very recent edit (cf https://github.com/gss/gss.github.io/commit/d6a931e3629d4b5d...).