Is this the normal speed of QJSEngine?

pablo_worker

Hi!

I am tinkering with the QJSEngine. As far as I understand, a QJSEngine instance will evaluate a JavaScript code passed to it. However, I am concerned about the computation speed of QJSEngine, it seems very slow.

My computer spends around 3-4 seconds computing this simple JavaScript code, is this normal?:

var X = [];
for (var i=0 ; i < 934600 ; ++i )
{
   X[i] = i;
}
X[120]

This is a simple code snippet of how I use QJSEngine.
Let's suppose that we have a button in the GUI, and when the button is pressed the following code is executed (it needs 4 seconds before the result is printed in the debug console):

void MainWindow::slot_ExecuteScript()
{
   QJSEngine myEngine;
   QString myScript = "var X = [];";
   myScript.append("for (var i=0 ; i < 934600 ; ++i ){X[i]=i;}");
   myScript.append("X[140]");
   QJSValue myValue = myEngine.evaluate(myScript);
   if(myValue.isError())
   {
      qDebug() << myValue.property("message").toString();
   }
   else
   {
      qDebug() << myValue.toString();
   }
}

Tested with Qt Creator 4.0.1. With Qt 5.7 MSVC2013 64 bits.

p3c0

@pablo_worker On Ubuntu 14.04 with Qt 5.6 and Qt 5.7 64 bits it is between 400 to 500 ms .

pablo_worker

Thank you!
The problem was that I was trying that in debug mode.
I have compiled again in Release mode and now its much faster!

Times (measured with QElapsedTimer)
In Debug mode: 3001 - 2999 ms.
In Release mode: 256 - 296 ms

10 times slower!