/**
 * 加載js文件
 * @param  {string || array}   url   js路徑
 * @param  {Function} fn      加載完成后回調
 * @return {object}           game對象
 * @example
 * getScript("url.js",fn)
 * getScript(["url-1.js","url-2.js"],fn)
 */
game.getScript = (function() {
 var cache = {};//內部緩存下url,下次則不請求
 return function(url, fn) {
  if ("string" === typeof(url)) {
   url = [url]; //如果不是數組帶個套
  };
  var i = 0,//循環起
   ok = 0,//加載成功幾個js
   len = url.length,//一共幾個js
   head = document.getElementsByTagName("head")[0],
   js, _url,
   create = function(url) {//創建js
    js = document.createElement("script");
    js.type = "text/javascript";
    js.src = url;
    head.appendChild(js);
    return js;
   };
  for (; i < len;) {
   if (cache[encodeURIComponent((_url = url[i++]))]) {//如果加載過
    (++ok >= len && fn) && fn();//如果加載完所有的js則執行回調
    continue;
   }
   cache[encodeURIComponent(_url)] = !0;//設置緩存
   js = create(_url);//創建js
   fn && (js.onload = function() {
    if (++ok >= len) {//如果加載完所有的js則執行回調
     fn();
    }
   });
  };
  head = js = _url = create  = null;
  return this;
 }
})();