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window.onload=function()
{
var img_x = document.getElementsByName("img_x"); //取出所有img_x
for(var i=0;i<img_x.length ;i++ )//循环
{
var imageArr=img_x[i]; 
var W = imageArr.width; 
var H = imageArr.height; 
var rate = W/H; 
if(W>H*rate){imageArr.style.width="121px";imageArr.style.height=121/rate+"px";alert(imageArr.style.width);alert(imageArr.style.height);} 
else{imageArr.style.height="135px";imageArr.style.width=135*rate+"px";} 
}

}