2 week newbie:- moving an image on rollover

Hi - i’m really new to this.

All I want to do is move an image a pixel at a time to the left on rollover on a button.

This is my script so far:

on (rollOver) {
background._x = background._x -=1;

This only moves it once then you have to take mouse off then rollover again to move again

What i’d like to incorporate is a loop so ( only whilst the mouse is over the button) the image keeps moving to a maximum of 300 pixels then it can’t move any more ( unless the right button has mouse over )

Help / advice, really appreciated. I’ve searched and searched and can’t find this basic procedure anywhere… :frowning: