property modified

This property sets and gets the document's internal "modified" flag. This can be used for things such as "save before exit".

function OnClosed()
{
    var bx = scene.getBoxById("htmlBox");
    if (bx)
    {
        if (bx.modified && PromptUserForDocSave())
        {
            var fileStrm = shell.serviceManager.basics.fileStream;
            fileStrm.openForWrite("C:\\myfile.html", true, true);
            bx.save(fileStrm, true);
            fileStrm.close();
        }
    }
}