executing a script [listener] on document size changes - like a variable

I would like to use variable to populate a text box with the document size, but Im not sure this is possible yet… so I've found a script which can be applied to a text frame and be executed through the scripts panel. But I was wondering if its possible a script can use something like an event listener to re-populate a text frame each time I change the document size. here is the code so far, thanks to the link Textvariable page size?

myDoc = app.activeDocument;
myPages = myDoc.pages.everyItem().getElements();
mhV = myDoc.viewPreferences.horizontalMeasurementUnits;
mvV = myDoc.viewPreferences.verticalMeasurementUnits;
myDoc.viewPreferences.horizontalMeasurementUnits = myDoc.viewPreferences.verticalMeasurementUnits = MeasurementUnits.MILLIMETERS;

for (var k = 0; k < myPages.length; k++) {
    resString = mySize(myPages);
    resFrame = myFrame(myPages);
    resFrame.contents = resString;
    }

myDoc.viewPreferences.horizontalMeasurementUnits = mhV;
myDoc.viewPreferences.verticalMeasurementUnits = mvV;

function mySize (page) {
    var Pbound = page.bounds;
    var pH = Pbound[2] - Pbound[0];
    var pW= Pbound[3] - Pbound[1];
    var res = (Math.round(pH*100)/100).toString() + "mm(H) x " + (Math.round(pW*100)/100).toString() + "mm(W)";
    return res;
    }

function myFrame (page) {
    var mF = page.textFrames.itemByName("pagesize");
    var arrSize = [62,30];
    return mF;
    }

(Label a text frame called pagesize in indesign)

can anyone help..

lister