How to do a “is_a”, “typeof” or instanceof in QML?

Since Qt 5.10, you can finally use instanceOf to check whether a variable is of a certain QML type, see “QML Support for Enum and InstanceOf Type Checks”.

import VPlayApps 1.0
import QtQuick 2.0

App {
  // two QML items, used for type checking
  Item { id: testItem }
  Rectangle { id: testRect }

  // function to check wheter an item is a Rectangle
  function isRectangle(item) {
    return item instanceof Rectangle
  }

  // type check example
  Component.onCompleted: {
    console.log("testItem is Rectangle? " + isRectangle(testItem))
    console.log("testRect is Rectangle? " + isRectangle(testRect))
  }
}