Please refer to: http://armand.eu/blog/working-with-measurement-units-in-adobe-extendscript

units_in_extendScript.jsx

// http://armand.eu/blog/working-with-measurement-units-in-adobe-extendscript/

function changeUnitsToPixels(){
  if(typeof originalUnitsH === 'undefined') originalUnitsH = app.documents[0].viewPreferences.horizontalMeasurementUnits;
  if(typeof originalUnitsV === 'undefined') originalUnitsV = app.documents[0].viewPreferences.verticalMeasurementUnits;
  app.documents[0].viewPreferences.horizontalMeasurementUnits = app.documents[0].viewPreferences.verticalMeasurementUnits = MeasurementUnits.pixels;
}

function changeUnitsBack(){
  app.documents[0].viewPreferences.horizontalMeasurementUnits = originalUnitsH;
  app.documents[0].viewPreferences.verticalMeasurementUnits = originalUnitsV;
  delete originalUnitsH;
  delete originalUnitsV;
}