QJSEngine won't evaluate js array correctly

Question

I have a file settings.js which includes an array with arrays of settings:

[
// [property, section, hex-address, Bytes to read/write, type, lsb, msb, options]

    ["AEC Control" , "AEC Control", 0x10300, 4, "bool", 0, 0],
    ["Shutter Mode", "Sensor Mode", 0x10104, 4, "bool", 0, 0],
    ["Nb ADC", "Sensor Mode", 0x10108, 4, "bool", 0, 0],
    ...
]

As you can see the file just contains the array value without assignment to a variable and without semicolon at the end.

The settings.js is put inside the resources.qrc:

<RCC>
    <qresource prefix="/js">
        <file alias="CameraSettings">resources/settings.js</file>
    </qresource>
</RCC>

I read the settings.js with QFile. Here is the code to evaluate the javascript:

QFile cameraSettingsJsFile(":/js/CameraSettings");
if(!cameraSettingsJsFile.open(QIODevice::ReadOnly | QIODevice::Text)) {
    throw std::exception("CameraSettingsProperties-file not valid!");
};

QJSEngine jsengine;
std::cout << "Output: '" << QTextStream(&cameraSettingsJsFile).readAll().toStdString() << "';" << std::endl;
QJSValue settingsArrayJSValue = jsengine.evaluate(QTextStream(&cameraSettingsJsFile).readAll());

Because of the Output line i know that the file is read correctly however QJSEngine won't evaluate the value correctly. Because settingsArrayJSValue.isArray() evaluates to false i called all is...() functions on settingsArrayJSValue. Only settingsArrayJSValue.isUndefined() evaluates to true.

I also tried this:

jsengine.evaluate("x=" + QTextStream(&cameraSettingsJsFile).readAll() + ";");

Then settingsArrayJSValue.isObject() evaluates to true (which is in a way expected when speaking of the js world) but i also get a SyntaxError: Expected token 'numeric literal'.

My final goal here is to parse the setttings array. Therefore i want to JSON.stringify the evaluated array and work with Qt QJson classes:

QJSValueList stringifyArguments;
stringifyArguments.append(settingsArrayJSValue);
QString evaluationResultString = jsengine
    .evaluate(QString("JSON.stringify"))
    .call(stringifyArguments)
    .toString();

QJsonArray jsonCameraSettingsArray = 
QJsonDocument::fromJson(evaluationResultString.toUtf8()).array();

Why does QJSEngine evaluates the valid array to undefined?

How can get QJSEngine to evaluate the array correctly so that i can process it further?

Answer 1

The problem was this line:

std::cout << "Output: '" << QTextStream(&cameraSettingsJsFile).readAll().toStdString() << "';" << std::endl;

Because i read the file there, when trying to read from cameraSettingsJsFile a second time QTextStream(&cameraSettingsJsFile).readAll() will be an empty string because the pointer is moved to the end of the stream.

So QJSEngine works fine...