检测浏览器是否支持AJAX

<script type="text/javascript"> 
function ajaxFunction() 
{ var xmlHttp; 
try { // Firefox, Opera 8.0+, Safari 
xmlHttp=new XMLHttpRequest();
 } 
catch (e) 
{ // Internet Explorer 
try { 
xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
 } 
catch (e) { 
try { 
xmlHttp=new ActiveXObject("Microsoft.XMLHTTP"); 
} catch (e) { 
alert("您的浏览器不支持AJAX！"); 
return false; 
} 
} 
} 
} 
</script>