Javascript: Load jQuery

loadjQuery.js

load = function() {
   load.getScript("http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js");
   load.tryReady(0); //用来等待jQuery类库加载
}

//以下代码用来动态加载任何js代码
load.getScript = function(filename) {
   var script = document.createElement('script')
   script.setAttribute("type","text/javascript")
   script.setAttribute("src", filename)
   if (typeof script!="undefined")
      document.getElementsByTagName("head")[0].appendChild(script)
}

load.tryReady = function(time_elapsed) {
//持续查询jQuery是否加载完毕
   if (typeof jQuery == "undefined") { // 如果没有加载jQuery...
      if (time_elapsed <= 5000) {
         setTimeout("load.tryReady(" + (time_elapsed + 200) + ")", 200); //设置200ms后继续尝试
      } else {
         alert("Failed to loading jQuery because of timeout.")
      }
   } else {
      // jQuery加载完毕后执行的代码
      alert("Great! jQuery is loaded.");
   }
}

load();