function changeTab(img_num, wrapper) {
    var imgs = document.getElementById(wrapper).getElementsByTagName("img");
    for(var i=0; i < imgs.length; i++) {
      if(imgs[i].src.indexOf("on.jpg") != -1 && img_num != i) {
        imgs[i].src = imgs[i].src.replace("on.jpg","off.jpg");
        document.getElementById(wrapper+"_tab"+i).style.display = "none";
      }
      if(img_num == i) {
        if(imgs[i].src.indexOf("off.jpg") != -1) {
          imgs[i].src = imgs[i].src.replace("off.jpg","on.jpg");
          document.getElementById(wrapper+"_tab"+i).style.display = "block";
        }
      }
    }
  }
  function checkForm() {
    if(document.getElementById("colors").selectedIndex==0) { alert("Please select a grip size"); return false; }
    if(/^-?\d+$/.test(document.getElementById("pqty").value)) {
      return true;
    } else {
      alert("Please enter in a valid quantity");
      return false;
    }
  }
  function changeBox(sel) {
    var sel = document.getElementById("colors");
    document.getElementById("qty").name = sel[sel.selectedIndex].value;
  }
  function changeImage(num,pcode) {
    var image = document.getElementById("large_image"); 
    image.src = "http://img.tennis-warehouse.com/new_big/"+pcode+"-"+num+".jpg";
  } 
  function loadEmptyImage(num) {
    var tdlist = document.getElementById("thumbs_panel").getElementsByTagName("td");
    var element = tdlist[num-1];
    element.innerHTML = "<div style='width:54px;height:92px;'></div>";
    element.style.background = "#ffffff";
  }