ajax中获取XMLHttpRequest对象的方法(IE/Firefox/chrome)

<script type="text/javascript">
function GetXmlHttpObject() {
var xmlHttp = null;
try {
// Firefox, Opera 8.0+, Safari
xmlHttp = new XMLHttpRequest();
} catch (e) { // Internet Explorer
try {
xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
}
}
return xmlHttp;
}
alert(GetXmlHttpObject());

</script>