登录中使用ajax判断用户是否存在
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=gb2312" /><title>无标题文档</title><script src="ajax.js" type="text/javascript"></script></head><body onload="form1.u_name.focus();"><form name="form1">用户名: <input type="text" id="u_name" onChange="callServer();" /><span id="test1"></span><br>密 码：<input type="password" /><input type="submit" name="submit" value="注册" /></form></body></html>
// JavaScript Documentvar xmlHttp = false;try {xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");} catch (e) {try { xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");} catch (e2) { xmlHttp = false;}}if (!xmlHttp && typeof XMLHttpRequest != 'undefined') {xmlHttp = new XMLHttpRequest();}function callServer() {var u_name = document.getElementById("u_name").value;if ((u_name == null) || (u_name == "")) return;var url = "userCheck.asp?name=" + escape(u_name);//查询地址 返回值为"已被注册"或"可以注册"xmlHttp.open("GET", url, true);xmlHttp.onreadystatechange = updatePage;xmlHttp.send(null); }function updatePage() { if (xmlHttp.readyState == 4) {if (xmlHttp.status == 200){ var response = xmlHttp.responseText;if (response == "true"){ test1.innerHTML="";}else{ test1.innerHTML = "用户名不存在,请重新输入！"; document.getElementById("u_name").value=""; document.getElementById("u_name").focus();}}else if(xmlHttp.status==500){ test1.innerHTML=xmlHttp.responseText; }}}<%@LANGUAGE="VBSCRIPT"%><%username = request.querystring("name")if (username = "ajax") thenresponse.write "true"elseresponse.write "false"end if%>