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);

I work with dozens of independent designers on collaborative projects, and those of us with Creative Cloud have to remember to save an IDML copy for those on earlier versions. And we often forget.

So I use this script. It runs when InDesign starts up. Then every time I save an InDesign document, it automatically saves an IDML copy alongside the INDD, in the background.

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?