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Comment by brundolf | Hacker News Reader

RN uses native controls (not a webview) and JS is plenty fast for most UI logic (it's almost never the bottleneck on slow web apps), so I would not expect performance to be a problem here

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React Native is much slower on Android than on iOS, sometimes by orders of magnitude. You can get things usable on a lower-end Apple device, but on a lower-end Android an optimized RN app is still unusable. Part of this is due to the JS interpreter available on Android (which FB has tried to replace). But I think it's also due to architectural issues in Android itself and the natural overhead that RN has being too much in a constrained environment.

The real reason is the shitty CPU on typical low-end to mid-end Androids. They suck at running JS. And I mean REALLY suck, as in 5-10 times slower than an iPhone.

I recently came across a ridiculous example of a high-end Chinese phone (700$) where one our web app's interactions that normally is near-instant, took 6s instead. Turns out that besides the generic issue of poor JS performance on Android (due to CPU), this particular manufacturer decided to deliver on their ridiculous battery life claims by...running all JS on a low energy CPU core.

Right. As much as people want to complain about Apple forcing WebKit/View on everyone, what it has enabled them to do is build specific hardware level optimizations in for JS and page rendering, which means you can get really good desktop-level performance even with an otherwise limited CPU/battery. Given Chrome's horrendous issues on MacOS, they are going to drain the battery as fast as possible and then blame it on Apple. Chrome users will then blame Apple for bad battery life.

> The real reason is the shitty CPU on typical low-end to mid-end Android

Well yeah would you expect it to be otherwise? These devices cost a fraction of an iPhone.

People in the US don't realize iPhones are luxury products for the majority of people in the world.

Read again: 700$.

I had read that but it was clearly an exception, no?

"by...running all JS on a low energy CPU core"

RN is quite inefficient and perf issues will not be obvious if using high end devices. Which is why Meta is working on Hermes:

https://engineering.fb.com/2019/07/12/android/hermes/

Hermes is already enabled by default in rn.

If you can get away with it, it's not a bad option. But it's still early days. If you run into compatibility problems or bugs with libraries being used, you could be in trouble.

That’s from almost 3 years ago. RN had changed a lot since then (and Hermes is included by default now)

https://reactnative.dev/architecture/bundled-hermes

I like your confidence but obviously you haven’t released an app in an Asian market. Performance is an issue here since most are using outdated Android phones from average of 5 years ago.

Exactly. Same with the LATAM market. Most are using old Android devices or sub $200 devices.

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