InDesign Startup Script that saves an IDML copy alongside INDD automatically

also-save-idml.js

// This InDesign Startup Script saves an IDML copy of the INDD file you're saving.
// Save it in your Startup Scripts folder. For how to do that, open the tutorial
// for your version of InDesign here: https://www.adobe.com/devnet/indesign/documentation.html
// and look for the section titled 'Installing scripts'.
// Thanks to fabiantheblind here http://graphicdesign.stackexchange.com/a/71736/67488
// for the original script, which I've adapted to work as a startup script.

// Set a targetengine to make this work
#targetengine "session"

function saveIDML() {
    // Exit if no documents are open.
    if(app.layoutWindows.length == 0) {
        return;
    } else {
        // Get the current document
        var doc = app.activeDocument;
        $.writeln('Saving IDML of ' + doc + ' ...');
        // Catch errors
        if (!doc.saved) {
          alert('Sorry, there was a problem and the document was not saved.');
          exit();
        }
        // Create a new .idml file name from the .indd file name
        var inddName = doc.name;
        var idmlName = inddName.replace("indd", "idml");
        // Create the new .idml file next to the .indd file
        var theFile = File(File(doc.filePath).fsName + "/" + idmlName);
        doc.exportFile(ExportFormat.INDESIGN_MARKUP, theFile, false);
    }
}
// Listen for the save event
app.addEventListener('afterSave', saveIDML, false);

Was just upgraded to CC 2017 and needed a script like this. It's working most of the time but occasionally having issues. I'll document them more as I test it. It launches the ExtendScript Toolkit app when saving in indesign. Has that been the case in the past?

@MCISTL Sorry, just saw your comment. Are you still having those issues?