[undefinedzero]

React/competitor performance that people use to compare frameworks is about rendering performance. E.g. React takes 100ms longer to rerender 10,000 elements (random numbers for the example). In these situations the actual real world difference will be negligible.

Site performance is much more API based, and that’s the same regardless of frontend. React has more library solutions to optimize the UX though, as it’s the most mature and popular.

[taylodl]

> Site performance is much more API based

Exactly. And those API calls are going out over the network. The caller has to serialize the request into text, the API implementation has to deserialize the text into values that can be passed to a local implementation function and then the API implementation has to take the result and serialize it into the return. Finally the caller has to process the result.

That's the simple case. Things get even more involved when you start using HTTPS to secure the data in transit on the channel and using OAuth to secure the access to the API. What appears to be a simple API call turns into a lot of back-and-forths with multiple servers - with all the network latency that entails. Then developers complain their website is slow. Gee, I wonder why!

[kunley]

Not exactly true about "performance is more API based". Everything adds up. 400ms here, 700 there. Websites can be slow even before api calls are triggered or on the middle of them, or while the results from api responses are presented.

[undefinedzero]

Rendering performance can definitely add up, but rarely do React websites render so many elements that you get to 700ms. Once you do, you can nearly always fix that with an performance optimizations iteration. I reckon that issue is just as likely in all frameworks, and less likely to be about React using 0.2ms (or something like that) longer per element to render before optimizations.

[jameshart]

People are tempted to use react in the animation frame render loop, and these comparisons often seem to assume that that is the level of performance we need to be targeting - enough to hold 60 fps. But react’s not a good fit there. Other animation techniques are better for a vast number of reasons.