Web Apocrypha

For some time it has been possible to build and run QtWebKit on Linux using Google's V8 JavaScript engine instead of the default JavaScriptCore. I thought it would be good to see some numbers comparing the runtime performance of the two engines in the same environment and also measuring the performance of the browser bindings.

The central data structure in JavaScriptCore is JSValue. It represents the value of a JavaScript variable. Since there are no type restrictions in JavaScript, a JSValue can contain anything from a simple bool constant to an object. Most operations work on these JSValues, so their effective handling is essential for a fast JavaScript engine. In JavaScriptCore there are 3 types of JSValue representations: JSValue32 and JSValue32_64 for 32 bit machines, and JSValue64 for 64 bit machines. Albeit maintaining all of these representations is a heavy burden, the feeling to have a fast JS engine is rewarding.