iframe(frame)能否实时读取网址?

Question

<iframe name="iframe1" src="3.htm"></iframe>
<script language=javascript defer>
var obj=document.getElementById("iframe1")
obj.onreadystatechange=function(){
if(this.readyState =="complete")
{
alert(window.frames["iframe1"].document.location.href)
}
}
</script>
<input name="button1" type="button" value="按" onclick="iframe1.document.location.href='4.htm'">
<input name="button1" type="button" value="按" onclick="iframe1.document.location.href='3.htm'">

Answer 1

<iframe src='....' id="f_1" onload="alert(this.src)"></iframe>