非IE浏览器：new XMLHttpRequest();
IE浏览器：new ActiveXObject('MicroSoft.XmlHttp');
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
<script type="text/javascript">
function getXhr() {
var xhr = null;
if (window.XMLHttpRequest) {
xhr = new XMLHttpRequest();
} else {
xhr = new ActiveXObject('MicroSoft.XmlHttp');
}
return xhr;
}
</script>
</head>
<body style="font-size:30px;">
<a href="javascript:alert(getXhr());">ClickMe</a>
</body>
</html>