Using the Qt API in Qt Script is very similar to C++.
var f = new QFile("foo.txt");
C++ enum values are mapped to properties of the script constructor function; e.g.
QIODevice::ReadOnly becomes QIODevice.ReadOnly.
f.open(new QIODevice.OpenMode(QIODevice.ReadOnly));
Each C++ flag type is mapped to a property of the script constructor function; e.g. QIODevice::OpenMode becomes QIODevice.OpenMode. Such a property is a constructor function that takes one or more enum values and constructs a flags instance by OR'ing the arguments together.
var ts = new QTextStream(f);
ts.writeString("Boo");
C++ streaming operators are normally mapped to readT() and writeT() functions.
f.close();
In Qt Script, all objects are allocated on the heap; objects that are no longer referenced are garbage collected sometime in the future; therefore, make sure to explicitly free up resources if you can. (Without the call to close(), the underlying file would remain open until the file object is garbage collected.)