function showCityWhether(str) {
xmlhttp=GetXmlHttpObject();
var url="http://weather.yahooapis.com/forecastrss?w=2442047&u=c";
xmlhttp.onreadystatechange=stateChanged;
xmlhttp.open("GET",url,true);
xmlhttp.send(null);
}

function stateChanged() {
if (xmlhttp.readyState== 4 ) {
  document.getElementById("txtHint").innerHTML=xmlhttp.responseText;
  alert("<" + xmlhttp.responseText + ">");
}
}

<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<rss version="2.0" xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0" xmlns:geo="http://www.w3.org/2003/01/geo/wgs84_pos#">
<channel>
  <title>Yahoo! Weather - Sunnyvale, CA</title>
  <link>http://us.rd.yahoo.com/dailynews/rss/weather/Sunnyvale__CA/*http://weather.yahoo.com/forecast/USCA1116_f.html</link>
  <description>Yahoo! Weather for Sunnyvale, CA</description>
  <language>en-us</language>
  ...
</channel>
</rss>