In Chromium you can turn off V8's JIT compiler for this reason. You can even opt in again for sites you trust that need the additional performance.
It’s only very heavy calculations that see a boost in performance. But, realistically, how many websites require this or currently use this today? <1%? Maybe <.1%?
This is pretty typical across JIT engines, too. PHP also sees only a slight increase in performance from the JIT. Because of the nature of PHP applications, most time is spend on the network and database. Only very CPU-heavy code sees a significant speed up.
That’s even the case for C#, which is why the dotnet runtime only conditionally JIT compiles code. Only hot path code is eligible for JIT compilation.
It still uses a WKWebView today, even in the EU, despite Apple now allowing alternative browser engines in the EU as of 2 years ago.
I'm sure Chrome will eventually ship Blink+V8 in the EU. It will take some time
In synthetic benchmarks, there was a 40-80% reduction in performance when disabling the JIT. But in a simulated test on YouTube.com, the performance delta was only 6%.
This isn’t the best source as it’s a bit old, and it wasn’t just JIT that was disabled. But the core idea is the same: calculation-heavy code can see an improvement, but most code won’t. Why this matters is how people actually use JS on the web. It’s not for cryptography and such, it’s to manipulate the DOM.
Microsoft also has some benchmarks here: https://microsoftedge.github.io/edgevr/posts/Super-Duper-Sec...
For PHP the RFC analyzes it: https://wiki.php.net/rfc/jit
We see a similar pattern: in synthetic benchmarks, the performance gain is large. But Wordpress, by far the largest PHP deployment in the wild, only saw ~3% performance gain. It again comes down to how PHP is used. It’s mostly HTML construction and database calls, neither of which will see any performance gain from a JIT. And, PHP has extensions, where most heavy code is moved to. Things like cryptography are done in PHP extensions, in C, where the JIT doesn’t matter. I’m more familiar with PHP, so I’ve known about the history of PHP not shipping a JIT due to the lackluster performance.
The only .NET implementations that interpret CIL were the .NET Compact and Micro frameworks due to hardware limitations, nowadays mostly gone as .NET workloads, and alternative implementations like Mono.