我这样获取iframe中的信息，但是提示有问题

Question

try:<iframe name="upload_frame" id="upload_frame" src="f.htm" ></iframe><script language="javascript">
<!--
alert(document.getElementById('upload_frame').document.body.innerHTML)
//-->
</script>

Answer 1

document.frames['upload_frame'].window.document.body.innerText; 

Answer 2

document.frames['upload_frame'].contentWindow.document.body.innerText; 通用

Answer 3

alert(document.getElementById('upload_frame').document.body.innerHTML)
你的代码有错