Is ReactJS really fast?

As I was mumbling to myself in a recent other HN comment, it has become clear to me that few people take the time to actually understand the speed differences between various technologies. Even as "everybody" says how benchmarks are useless, "everybody" still uses the most trivial microbenchmarks to decide what's fast. (Perhaps the uselessness of benchmarks has more to do with "everybody" taking cognitive shortcuts than the benchmarks themselves....)

Amusingly, this produces the result that almost every technology is faster every other tech, with the exception of the technologies that are vastly more powerful than something else, but still at least as fast (i.e., Python is at least as fast as C at some task, so it must be as fast as C in general, right?).

(The natural reaction to that is to assume that there is no such thing as speed differences, but, alas, that's not true either. No easy answers! There are things that are faster than other things at some tasks. And there are jobs where you really need to know which is which because even today, the difference between a 50-node cluster and 1 machine that does it all is quite monetarily significant....)

React.js is actually just really pleasant to work in and easy to reason about, and the virtual DOM is what makes that all possible without it becoming unacceptably slow. DOM diffing isn't there to make React faster than everything else ever imagined. It's there to let you stop thinking about the DOM and focus on the world state of your frontend instead.

I wasn't truly interested in React until I read this, which does a better job of spelling out React's real advantages than I ever could: http://jlongster.com/Removing-User-Interface-Complexity,-or-...

Here's a choice quote:

"Rerendering everything (and only applying it to the DOM when something actually changed) vastly simplifies the architecture of our app. Observables+DOM elements is a leaky abstraction, and as a user I shouldn't need an intimate knowledge of how the UI is kept in sync with my data. This architecture opens up lots of various ways to optimize the rendering, but it's all completely transparent to the user."

It's not everything is about speed, I would choose manageability over speed anytime

I think the bigger appeal of React isn't the "performance." It's the fact that you can reason about your app as if you are re-rendering the entire application with every change in state. That way you never have to think about mutating the DOM, and you have less places to screw up.

If you actually re-rendered the whole app with every state change, it wouldn't be performant, but with the virtual DOM, it's totally feasible. It is definitely unfortunate that developers take statistics for granted (I'm guilty of this), but it doesn't undermine the usefulness of the framework.

I really don't like Angular (mostly down to dependency injection, issues I had getting some of the components to work with mobile and it's markup ngAttributes mess) and it put me off React until recently. React is superb and a really new way of thinking about user interface components.