iframe自定义高度

function setIframeHeight()
{
  var iframe=document.getElementById("iframe_id");
  iframe.height="500px";//默认高度为500
  var subcontent=document.frames?  document.frames["iframe_id"].document:iframe.contentDocument;
  setHeight=Math.max(subcontent.body.scrollHeight,subcontent.documentElement.scrollHeight);
iframe.height=setHeight;
}