Does Silverlight have a performance advantage over JavaScript?

Speculating is fun. Or we could actually try a test or two...

That Silverlight vs. Javascript chess sample has been updated for Silverlight 2. When I run it, C# averages 420,000 nodes per second vs. Javascript at 23,000 nodes per second. I'm running the dev branch of Google Chrome (v. 0.4.154.25). That's still almost an 18x speed advantage for Silverlight.

Primes calculation shows a 3x advantage for Silverlight: calculating 1,000,000 primes in Javascript takes 3.7 seconds, in Silverlight takes 1.2 seconds.

So I think that for calculation, there's still a pretty strong advantage for Silverlight, and my gut feel is that it's likely to stay that way. Both sides will continue to optimize, but there are some limits to what you can optimize in a dynamic language.

Silverlight doesn't (yet) have an advantage when it comes to animation. For instance, the Bubblemark test shows Javascript running at 170 fps, and Silverlight running at 100 fps. I think we can expect to see that change when Silverlight 3 comes out, since it will include GPU support.

I'd say that architecturally, it's a wash.

On the one hand Silverlight is MSIL code, which is reasonably fast compared to raw, optimized native code but still runs slower due to the VM (CLR) overhead and will still have slow initial load times when being ngen'd.

On the other hand the speed of Javascript is much less reliable due to the huge variations in Javascript engines which have an order of magnitude, or more, range in performance. You have slow interpreters like IE, though IE8 is speeding things up, and then you have faster compilers/interpreters like SpiderMonkey and V8 which have only recently begun to explore the performance limits of Javascript. There's also new technologies in the R&D phase like TraceMonkey which have tremendous potential to vastly improve Javascript performance (getting close to native code speeds). Javascript does have the inherent disadvantage that it is single-threaded, but given the difficulty of writing good threaded code it's hard to say how much difference that makes.

At the end of the day when comparing apples to apples the real performance bottleneck is the DOM, and there it doesn't much matter what technology you're using to manipulate it.

Javascript is ran in a virtual machine by most browsers. However, Javascript is still a funky language, and even a "fast" virtual machine like V8 is incredibly slow by modern standards.

I'd expect the CLR to be faster.