http://www.w3schools.com/jsref/event_onload.asp
onload is most often used within the <body> element to execute a script once a web page has completely loaded all content (including images, script files, CSS files, etc.).
http://www.cnblogs.com/xiaohuochai/p/4859899.html
给图片增加data-original = "img/test.jpg"的属性，保存图片的真实地址
<img src="loading.gif" w_src="w_img_url" > <script> window.onload = function(){ var w_imgs = document.images; len = w_imgs.length; for(var w = 0; w<len; w++){ var w_img = w_imgs[w]; var w_img_src = w_img.getAttribute('w_img_src'); w_img.src = w_img_src; } } </script>