initOrder.qml

import QtQuick 2.1


Item {
  id: root
  
  Item {
    id: a
    property var prop: console.log("a.prop property defined")
    Component.onCompleted: console.log("a complete")
    
    Item {
      id: aa
      property var prop: console.log("aa.prop property defined")
      Component.onCompleted: console.log("aa complete")
    }
    
    Item {
      id: ab
      property var prop: console.log("ab.prop property defined")
      Component.onCompleted: console.log("ab complete")
    }
  }
  
  Item {
    id: b
    property var prop: console.log("b.prop property defined")
    Component.onCompleted: console.log("b complete")
    
    Item {
      id: ba
      property var prop: console.log("ba.prop property defined")
      Component.onCompleted: console.log("ba complete")
    }
    
    Item {
      id: bb
      property var prop: console.log("bb.prop property defined")
      Component.onCompleted: console.log("bb complete")
    }
  }
  
  property var prop: console.log("root.prop property defined")
  Component.onCompleted: console.log("root complete")
}

output

qml: bb.prop property defined
qml: ba.prop property defined
qml: b.prop property defined
qml: ab.prop property defined
qml: aa.prop property defined
qml: a.prop property defined
qml: root.prop property defined
qml: root complete
qml: b complete
qml: bb complete
qml: ba complete
qml: a complete
qml: ab complete
qml: aa complete