Qt Labs Blogs » Lightning-fast JavaScript

Here are the performance numbers about Qt4.5’s improvement in JavaScript performance that I mentioned in yesterday’s post. It offers about a seven times performance improvement on ix86 processors. From Lightning-fast JavaScript:

For Qt 4.5, the JavaScript engine is powered by a new bytecode interpreter, along with optional JIT (just-in-time) compile support. They are often referred as SquirrelFish and SquirrelFish Extreme, respectively. This interpreter has been developed by Apple engineers working on WebKit in order to speed-up JavaScriptCore, the backbone of WebKit’s JavaScript engine. The interpreter makes its first appearance in the recent Safari 4 Public Beta, where it is dubbed as Nitro JavaScript Engine.

Longer is better:


Qt 4.5 released


Qt is now released under the Lesser General Public License meaning it can be freely linked into commercial applications.


Read What’s New or a more detailed description to see what’s changed since Qt 4.4 (released in May, 2008).

  • If you haven’t upgraded to Qt4, here’s what changed since Qt 3.3.4 in June, 2005.

  • Latest WebKit (aka the html display used by Apple’s Safari browser) including support for Netscape plug in so, for example, Flash can be embedded. Includes HTML 5 and CSS animation.

  • XSLT support (XML translation)

  • QtCreator is a Visual Studio like editor that works cross platform and incorporates debuging support and Qt Designer (a layout editor).

  • Mac OS X Cocoa support (latest Mac graphics library). Enables 64-bit support.


Read either Improved Performance or a white paper with more details and it requires registration so they can email it to you.

  • FileDialog is significantly faster (60x in one case)

  • QGraphicsView optimized

  • Clipping sped up.

  • Added SquirrelFish javascript engine which is much, much faster.

  • Added QtBenchLib to make application performance testing easier.


A few other noteworthy changes: