无阻塞的JS加载模式

LazyLoad

<script type="text/javascript">
function loadScript(url,callback){
  var script = document.createElement("script"),
      script.type = 'text/javascript';

  if(script.readyState){ //ie
    script.onreadystatechange = function(){
      if(script.readyState == 'loaded' || script.readyState == 'complete'){
        script.onreadystatechange = null;
        callback();
      }
    }
  }else{
    script.onload = function(){
      callback();
    };
  }

  script.src = url;
  document.getElementByTagName('head')(0).appendChild(script);
}
</script>