Qt Quick Compiler▲
The Qt Quick Compiler consist of two components:
The QML Type Compiler (qmltc) compiles QML object structures into C++ classes. The QML Script Compiler compiles functions and expressions in QML files of an application into C++ code.
qmltc uses an all-or-nothing approach, and compilation simply fails if some unsupported language feature is encountered.
In the case of qmlsc JavaScript sets limitations on compiling with qmlsc. For more information see Limitations when compiling JavaScript.