At first glance, this seems much better in terms of programmer productivity, given that it uses logicless templates rather than embedding HTML inside JS code. But I'd be curious if it's less performant.
React and Blaze both compile templates or components into an intermediate representation for their HTML structure (React's JSDOM; Blaze's HTMLJS). A lot of the difference in how they decide what DOM changes are necessary.
React re-renders components when data changes and diffs the resulting JSDOM. The diff algorithm is fast and has simple hooks to make it faster by letting you compare state and component properties.
Blaze doesn't diff the resulting DOM structure. Instead, Blaze diffs the data the components depend on. That data comes from reactive functions built on top of Deps, our dependency tracking system. When the component first renders, dependencies are tracked between data sources and rendered DOM elements (dependencies are automatically cleaned up when the component is taken off the page). Therefore when data changes, Blaze can directly update the relevant elements.
There is some overhead in Deps, our dependency tracking system, but Deps has been intentionally designed for supporting this efficiently (eg batching updates in a "flush" stage).
As for performance, our benchmarks have generally found that React outperforms Blaze when many elements change and Blaze outperforms React when few elements change (which is more common for typical operations on many web apps). We also have plans to improve performance on initial rendering.
There are some other difference worth noting: While a later version of Blaze will support easy APIs for re-useable components, React already has one. And the React component model is well-thought out, complete and in production use whereas the Blaze component model at the moment is only the implementation behind templates.
Happy to hear any other perspectives.
Nevertheless, seriously appreciate the detailed and informative response. :)
React by default is fairly fast but what makes it stand out is that it gives the tools to make the bottlenecks faster without having to drop the nice abstraction.
You have a lot less control over the performance of your app with data binding.
FWIW this is available to React as an optimisation if desired/necessary: by default React just renders the whole component tree on data changes[0] and diffs the result tree before updating the DOM — which is simple and usually performs well — but components can implement shouldComponentUpdate[1] to skip re-rendering if unnecessary[2].
[0] a React component could depend on non-react data, React is conservative and does not assume components depend only on data it can track
[1] http://facebook.github.io/react/docs/component-specs.html#up...
[2] and React provides ReactComponentWithPureRenderMixin[3] which can be mixed into any "pure" component whose output depends solely on application and component state, to get a free shouldComponentUpdate
[3] well "provides" may be excessive, it's in the repository but seems to be neither in the react distribution nor in the react-with-addons distribution. YMMV.
Here is one of the React core developers (Pete Hunt) on React integration with Meteor: http://www.youtube.com/watch?v=qqVbr_LaCIo (note this is before Blaze)
Regarding performance: https://groups.google.com/forum/#!topic/meteor-core/-px_AGhj...
React will probably be easier to reason about down the line (despite the initial learning curve), while Blaze will "just work".