QMLSC warnings about untyped JavaScript list-related untyped functions

Run the attached reproducer on Ubuntu, Qt 6.5.0, and QMLSC will complain about untyped JavaScript functions:
Warning: main.qml:19:23: Could not compile function getText: Cannot generate efficient code for call to untyped JavaScript function [compiler]
Warning: main.qml:36:77: Could not compile binding for onCompleted: Cannot generate efficient code for call to untyped JavaScript function [compiler]

Clearly, QMLSC cannot convert shift() and indexOf() to efficient C++ codes.

I guess this kind of QMLSC-related issue is a part of this massive task:
https://bugreports.qt.io/browse/QTBUG-76025