#include <QtQml>

int main(int argc, char *argv[])
{
    QCoreApplication app(argc, argv);

    QQmlEngine engine;

    QByteArray data = "{ \"foo\":\"bar\" }";
    engine.rootContext()->setContextProperty("byteArrayData", data);
    engine.rootContext()->setContextProperty("stringData", QString::fromUtf8(data));

    QQmlComponent component(&engine);
    component.setData("import QtQml 2.0; QtObject { Component.onCompleted: JSON.parse(stringData) }", QUrl("string"));
    component.create(); // ok

    component.setData("import QtQml 2.0; QtObject { Component.onCompleted: JSON.parse(byteArrayData) }", QUrl("bytearray"));
    component.create(); // bytearray:1: JSON.parse: Parse error
}