Property-var

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QtQuick 1.x

  • There was no javascript var type property, but property variant, internally a QVariant.
  • Assigning a JavaScript object to that property would result in it being converted to a QVariantMap.
  • Accessing that property from JS would result in that QVariantMap being converted back into a JS object.
  • JS function reference, special JS values (null, undefined) could not be stored in the 'property variant' type of property.

QtQuick 2.0

  • Deprecated "property variant" and added "property var; internally they are javascript values.
  • Support storing of anything created in JS, including JS function references.
  • Only when accessed from C++ (via QObject::property() or QQmlProperty::read()) will be converted to a QVariant (same conversions rules of any other JS value to QVariant conversion apply).
  • When implementing types on the C++ side, one can use the QJSValue class as a property/method parameter to transfer values between C++ and QML/JS without type/data loss.
    • Includes JS functions; for example, you can assign a function to a property from QML and call it later from C++ using QJSValue::call().