Me: It is still a lot slower than ActionScript.
Developer: Oh don't quote me old numbers, the new browsers are so much faster.
Me: Still slower than ActionScript.
Developer: Maybe slower at doing useless things like calculating prime numbers. Who would do that in a browser anyways? The new browsers are fast at doing realistic things.
Me: But still slower than ActionScript.
Developer: Show me some proof on something realistic, like parsing XML coming back from an Ajax call.
Me: [Whips together a servlet for producing huge chunks of XML and some JS and a SWF for calling it and doing a DOM parse.] Alright let's see the results of these tests...
Everything is O(N), as you would expect, and can verify by doing a linear regression of XML document size vs. parse time. Safari 4 is much faster than Firefox 3, the ratio of their slopes (FF3/S4) = 2.95. But they both lose badly to ActionScript 3 (running Flash Player 10, RC2), (FF3/AS3) = 6.36 and (S4/AS3) = 2.16. Maybe IE can do better, should we give it a try?
Developer: Now you are being a jerk.