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# 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 (opens new window) chapter in the Qt documentation.