js去除浏览器默认底图的方法

function addListener(element, type, expression, bubbling) {
 bubbling = bubbling || false;
 if(window.addEventListener) { // Standard
 element.addEventListener(type, expression, bubbling);
 return true;
 } 
 else if(window.attachEvent) { // IE
 element.attachEvent('on' + type, expression);
 return true;
 } 
 else return false;
}
var ImageLoader = function(url){
 this.url = url;
 this.image = null;
 this.loadEvent = null;
};
ImageLoader.prototype = {
 load:function(){
 this.image = document.createElement_x('img');
 var url = this.url;
 var image = this.image;
 var loadEvent = this.loadEvent;
 addListener(this.image, 'load', function(e) {
  if(loadEvent != null){
  loadEvent(url, image);
  }
 }, false);
 this.image.src = this.url;
 },
 getImage:function(){
 return this.image;
 }
};
function loadImage(objId,urls) {
 var loader = new ImageLoader(urls);
 loader.loadEvent = function(url){
 obj = document.getElementByIdx_x(objId);
 obj.src = url;
 }
 loader.load();
}

<img id="loading1″ src="loading.gif" />
<script language="javascript">
loadImage("loading1″,"http://.baidu./img/baidu_logo.gif");
</script>