> For the complete documentation index, see [llms.txt](https://docs.novaflowos.com/start/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.novaflowos.com/start/qt6-qml-book/readme/ch04-qmlstart/advanced.md).

# Advanced Techniques

## Performance of QML

QML and Javascript are interpreted languages. This means that they do not have to be processed by a compiler before being executed. Instead, they are being run inside an execution engine. However, as interpretation is a costly operation, various techniques are used to improve performance.

The QML engine uses just-in-time (JIT) compilation to improve performance. It also caches the intermediate output to avoid having to recompile. This works seamlessly for you as a developer. The only trace of this is that files ending with `qmlc` and `jsc` can be found next to the source files.

If you want to avoid the initial start-up penalty induced by the initial parsing you can also pre-compile your QML and Javascript. This requires you to put your code into a Qt resource file, and is described in detail in the [Compiling QML Ahead of Time](https://doc.qt.io/qt-6/qtquick-deployment.html#ahead-of-time-compilation) chapter in the Qt documentation.