Get login name/password in popup and return result

initial.html: 
<SCRIPT LANGUAGE="JavaScript"><!--
var loginname = '';
var loginpassword = '';
function windowOpen() {
  var myWindow=window.open('popup.html','windowRef','width=200,height=200');
  myWindow.location.href = 'popup.html';
  if (!myWindow.opener)
    myWindow.opener = self;
}
function go(url) {
  location.href = url + '?' + loginname + '&' + loginpassword;
}
windowOpen();
//--></SCRIPT>
<A HREF="javascript:go('nextpage.html')">go to next page</A>
 

popup.html: 
<SCRIPT LANGUAGE="JavaScript"><!--
function returnDetails() {
  opener.loginname = document.myForm.loginname.value;
  opener.loginpassword = document.myForm.loginpassword.value;
  self.close();
}
//--></SCRIPT>
<FORM NAME="myForm">
Name: <INPUT TYPE="TEXT" NAME="loginname">
Password: <INPUT TYPE="PASSWORD" NAME="loginpassword">
<INPUT TYPE="BUTTON" VALUE="ENTER" onClick="returnDetails()">
</FORM>
 

nextpage.html: 
<SCRIPT LANGUAGE="JavaScript"><!--
var start = location.search.indexOf('?');
var end  = location.search.indexOf('&');
var loginname = location.search.substring(start+1,end);
var loginpassword = location.search.substring(end+1);
alert('Name = ' + loginname + '\n' + 'Password = ' + loginpassword);
//--></SCRIPT>
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