Javascript setInterval unwanted pause -

i trying create animation few images in javascript , have code working, after runs through images in reverse pauses before starts going forward again. i'm wondering how rid of pause?

here code in action http://isogashii.com/projects/javascript/ch10/dp10-6.html

html

<img id="pin" src="assets/pin0.gif" alt="pin animation" /> 

javascript

var pin = new array(9); var curpin = 0; var x = false;  // caching images (var imagesloaded=0; imagesloaded < 9; ++imagesloaded) {     pin[imagesloaded] = new image();     pin[imagesloaded].src = "assets/pin" + imagesloaded + ".gif";      //starts pinf function when images cached     if (imagesloaded == 8) {         setinterval("pinf()", 120);     } }  function pinf() {      if (x == true) {         --curpin;         if (curpin == 0) {             x = false;         }     }     if (x == false) {         ++curpin;         if (curpin == 8) {             x = true;         }     }      document.getelementbyid("pin").src = pin[curpin].src; } 

in x == true portion of if statement, should set curpin 1 otherwise duplicating curpin = 1.

http://jsfiddle.net/a77cx/

function pinf() {      if (x == true) {         --curpin;         if (curpin == 0) {             curpin = 1;             x = false;         }     }     if (x == false) {         ++curpin;         if (curpin == 8) {             x = true;         }     }      document.getelementbyid("pin").src = pin[curpin].src; }