code: function updateSingleArray(aOrig, aAdditional, bRemove) {
  		if (!aAdditional) {
  			return;
  		}
  
  		for (var i = 0; i < aAdditional.length; i++) {
  			var iIndex = aOrig.indexOf(aAdditional[i]);
  			if (iIndex > -1 && bRemove) {
  				aOrig.splice(iIndex, 1);
  			} else if (iIndex === -1 && !bRemove) {
  				aOrig.push(aAdditional[i]);
  			}
  		}
  	}
docs: update the single array for observing and unobserving