Ajax应用简单示例

<script language="JavaScript" type="text/javascript">
/* Create a new XMLHttpRequest object to talk to the Web server */
var xmlHttp = false;
/*@cc_on @*/
/*@if (@_jscript_version >= 5)
try {
xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try {
xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
} catch (e2) {
xmlHttp = false;
}
}
@end @*/

if (!xmlHttp && typeof XMLHttpRequest != "undefined") {
xmlHttp = new XMLHttpRequest();
}
function checkUser(userId){
try{
var userObj = document.getElementById(userId);
var url = "test.asp?username=" +escape(userObj.value);
xmlHttp.open("GET", url, true);
xmlHttp.onreadystatechange = checkUserOk;
xmlHttp.send(null);
}catch(exception){}
}
function checkUserOk(){
if (xmlHttp.readyState == 4) {
try{
var response = xmlHttp.responseText;
var alertObj = document.getElementById("reg_alert");
alertObj.innerHTML=response;
}catch(exception){}
}
}

</script>
<form name="form1" action="" method="post">
City<input type="text" name="username" id="username" size="25" >
<input type="button" name="check" value="检查唯一性" onClick=" checkUser('username')">
<span id="reg_alert" class="red_txt"> </span>
</form>
test.asp

<%
Response.ContentType = "text/html"
Response.Charset = "GB2312"
username=trim(request("username"))
if username="aaa" then
response.Write("ok")
else
response.Write("false")
end if

%>