<img id="graphics" src="images/graphic1.svg" />

<script type = "text/javascript">
(function() {     // function expression closure to contain variables
var i = 0;
var pics = [ "graphic1.svg", "graphic2.svg", "graphic3.svg" ];
var el = document.getElementById('graphics');  // el doesn't change
function toggle() {
    el.src = pics[i];           // set the image
    i = (i + 1) % pics.length;  // update the counter
}
setInterval(toggle, 3000);
})();             // invoke the function expression
  </script>