It is actually not the fact that V8 in context of Sciter alike use cases will be faster.
Consider this statement:
document.body.patch(<body>Hello world</body>);
In case of Sciter this expression runs with native speed. JSX is built-in and element.patch() method is native.
While in browser, in case of ReactJS, you will run that patch() (reconciliation procedure ReactDOM.render) with JS VM speed as that algorithm is implemented on JS/TS.
My guess is probably the QuickJS has less resource usage compared to the more performant V8.
UPDATE:
Now I have read the linked article, here is the reasons (copied from the article):
API and integration principles are close to what TIScript uses – it took me just 1 month to add QuickJS to Sciter core. And 4 months more to expose HTML/CSS runtime to JS.
Relatively compact implementation – QuickJS is slightly more fatty (by 100 kb) but still in acceptable range. For the note: full version of V8 is about 40 mb – 5 times larger than Sciter itself;
Liberal MIT license. Sciter cannot use GPL/LGPL code – many customers expressed this requirement;
There is a section with the key reasons it was picked, in particular:
"Relatively compact implementation – QuickJS is slightly more fatty (by 100 kb) but still in acceptable range. For the note: full version of V8 is about 40 mb – 5 times larger than Sciter itself"
40mb is just nuts. These days, jlink would allow me to shrink a Java JVM down to something like that. And that would already include some nontrivial batteries, which Javascript doesn't AFAIK.
Pure V8 - yes, close to 8 Mb - that is still larger than whole Sciter that beside of script VM contains HTML/CSS/Graphics, etc.
40 Mb came from Node.JS distribution (V8 + native runtime = node.exe).
Sciter is more comparable to NodeJS as it includes good chunk of NodeJS alike runtime too.
While I appreciate the conscious size-saving effort, I need to ask: is 30 MB difference that big of a deal for desktop applications nowadays? A random Electron app that I download will easily take up hundreds of MBs disk space.
I personally don’t think it’s acceptable and the disregard for files sizes generally extends to disregard for RAM usage which is even more unacceptable. Sadly I don’t really have a choice regarding using most of these apps.
Is it even possible to distill V8 into a single Windows DLL anymore? The version I use was about 3.5 MB in 2013. I tried updating it a couple of years ago, but quickly gave up and backed away, groping for the doorknob.
It's possible though not straight-forward. React Native Windows seems to have a version of V8 wrapped with JSI (for use in React Native) though by the looks of the project, it appears to be only used internally and not really meant for stand-along consumption: https://github.com/microsoft/v8-jsi
I wonder what are the global scale environmental consequences will be, long term. Could it make a difference between couple nuclear reactors urgently needed and no longer needed?
