use selectedIndex from select list

[zawadi]

Ok, I'm using PHP/javascript and for the most part works.

but in IE I have some javascript that doesn't, I know where it breaks but dont know how to fix

 

function validate_cat(cat) {
var http = false;

if(navigator.appName == "Microsoft Internet Explorer") {
	http = new ActiveXObject("Microsoft.XMLHTTP");
} else {
	http = new XMLHttpRequest();
}

//	document.frmjob.selpri.list = 0;
http.abort();
http.open("GET", "/logic/pri.php?cat=" + cat, false);
http.onreadystatechange=function() {
	if(http.readyState == 4) {
		document.frmjob.selpri.options.length=0;
		document.getElementById('selpri').innerHTML = http.responseText;
	}
}
http.send(null);
alert(document.frmjob.selcat.options[document.frmjob.selcat.selectedIndex].value);
-->	alert(document.frmjob.selpri.options[document.frmjob.selpri.selectedIndex].value); <--
alert(document.frmjob.oldcomp_by.value);
validate_pri(document.frmjob.selcat.options[document.frmjob.selcat.selectedIndex].value, document.frmjob.selpri.options[document.frmjob.selpri.selectedIndex].value, document.frmjob.oldcomp_by.value);
document.frmjob.selpri.focus();
}

 

the arrows show what breaks.

it seems that I cant use the index from a select list that has had its innerHTML reset, HELP please