前端js第一次加载未生效的问题

前端js第一次加载未生效，但是下次或下几次刷新都会生效

猜测：
1、有js加载报错导致需求js没有加载
2、

var forEach = function(array, callback, thisObject){
if(array.forEach){
array.forEach(callback, thisObject);
}else{
for (var i = 0, len = array.length; i < len; i++) { callback.call(thisObject, array[i], i, array); }
}
}

var st = new SlideTrans("idContainer2", "idSlider2", 2, { Vertical: false });

      var nums = [];
      //插入数字
      for(var i = 0, n = st._count - 1; i <= n;){
          (nums[i] = _get("idNum").appendChild(document.createElement("li"))).innerHTML = ++i;
      }

      forEach(nums, function(o, i){
          o.onmouseover = function(){ o.className = "on"; st.Auto = false; st.Run(i); }
          o.onmouseout = function(){ o.className = ""; st.Auto = true; st.Run(); }
      })

      //设置按钮样式
      st.onStart = function(){
          forEach(nums, function(o, i){ o.className = st.Index == i ? "on" : ""; })
      }
      st.Run();

正常：

1、forEach(nums, function(o, i){ o.className = st.Index == i ? "on" : ""; })
2、array.forEach(callback, thisObject);
3、结束
不正常：

1、forEach(nums, function(o, i){ o.className = st.Index == i ? "on" : ""; })
2、array.forEach(callback, thisObject);
3、forEach(nums, function(o, i){ o.className = st.Index == i ? "on" : ""; })
4、forEach(nums, function(o, i){ o.className = st.Index == i ? "on" : ""; })