How many JavaScript engines does a browser need? For Mozilla (with Spider/Jaeger Monkey) apparently they need one more.
The Narcissus engine is a testing engine of sorts that is supposed to enable developers to modify the engine in ways that Spider/Jaeger Monkey can not. Zaphod (named I suppose after the Hitchiker’s Guide to the Galaxy character Zaphod Beeblebrox, former president of the universe) is the add-on for Firefox 4 that enable Narcissus to run as a seperate JavaScript engine on the browser.
“With the Zaphod addon, you can also integrate Narcissus into the
browser as your JS engine in order to do some real meaningful tests,” Mozilla developer Tom Austin blogged. “Also, since your changes will be separate from the browser code base,
you can more easily share your ideas with others.
Zaphod will process any script tag with a type of “application/narcissus” using the Narcissus engine.”
An interesting idea, though I’m not sure how practically useful it will be for non-browser developers. In my (very) limited view, it is the specific default JavaScript engine in a given browser that is the key and yes performance does matter. That said, I’ve never before seen a browser vendor open up this kind of choice and with choice comes the opportunity for unforeseen innovation.
