var img_onload = function(){
	
	var _lazyImgs = [];
	
	//获取对象的 top值
	function getElementTop(elm){
		var flag = elm;
		var top = flag.offsetTop;
		while(flag = flag.offsetParent){
			top +=	flag.offsetTop;
		}	
		return top;
	}
	
	//获取延迟加载图片对象
	function getLazyImgs(){
		var imgs = document.getElementsByTagName("img");
		var lazyImgs = [];
		for( var i = 0; i < imgs.length; i ++){
			if( imgs[i].getAttribute("_src") ){
				
				lazyImgs.push(imgs[i]);
					
			}	
		}
		return lazyImgs;	
	}
	
	//延迟加载检测 imgs必须有 lazy_img 属性
	function imgOnLoadCheck(imgs){
		var imgGroup = imgs;
		function imgCheck(){
			if(imgGroup.length<=0){return;}	
			var screenHeight = document.documentElement.clientHeight;
			var screenScrollTop = document.documentElement.scrollTop||document.body.scrollTop;
			for( var i = 0; i < imgGroup.length;){
				if(!imgGroup[i].screenTop){
					imgGroup[i].screenTop =  getElementTop(imgGroup[i]);
				}
				if( getElementTop(imgGroup[i]) >= screenScrollTop && getElementTop(imgGroup[i]) <= screenScrollTop + screenHeight){
					imgGroup[i].src = imgGroup[i].getAttribute("_src");
					imgGroup.splice(i,1);
				}
				else{
					i++;	
				}		
			}
			setTimeout(imgCheck,200)
		}
		imgCheck();	
	}
	
	return{
		//函数执行
		init:function(){
			_lazyImgs = getLazyImgs();	
			
			imgOnLoadCheck(_lazyImgs);
			//alert(getElementTop(_lazyImgs[1]))	
		}	
	}	
}