Javascript控制iframe的url適用IE,google,FF

<script>
var iframe;
function set_status() {
iframe = document.getElementById("iframe");
iframe.onload = iframe.onreadystatechange = iframeload; 
iframe.src = "http://tw.yahoo.com";
}


function iframeload() {
if (!iframe.readyState || iframe.readyState == "complete") {
alert("Local iframe is now loaded.");
}
}
</script>
<iframe id="iframe" name="iframe">