Can read parent Properties from Javascript but not per Bindings - Bug or Feature?

[LowLevelM]

[PropRoot.qml]

import QtQuick 2.0

Item {
    property int propRoot: 123

    Timer {
        interval: 500
        running: true
        repeat: true
        onTriggered: propRoot = propRoot+1
    }

    PropChild {
    }
}

[PropChild.qml]

import QtQuick 2.0

Item {
    //property int propFromRoot: propRoot // ReferenceError: propRoot is not defined (as excepted)

    function func(n){
        console.log("propRoot: "+propRoot); // gets access to the current value???
    }

    Timer {
        interval: 500
        running: true
        repeat: true
        onTriggered: func()
    }
}

prints 123,124,125 etc.

Is that a bug because it breaks the scoping or a needfull feature?

[GrecKo]

That's not a bug and it is a documented behaviour ( https://doc.qt.io/archives/qt-5.6/qtqml-documents-scope.html#component-instance-hierarchy ) called dynamic scoping.

But keep it mind it's considered bad practice and might be removed in Qt 6.

In your case you should have in PropChild:

property int propFromRoot: propRoot

and use it like so in PropRoot:

id: root
property int propRoot: 123
/* ... */
PropChild {
    propFromRoot: root.propRoot
}