Ajax使用示例（不详细）

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var xmlHttp;

if(window.XMLHttpRequest){ //不是ie

xmlHttp = new XMLHttpRequest();

}else if(window.ActiveXObject){ //ie

xmlHttp =new ActiveXObject("Microsoft.XMLTHHP");

}

var url = "user_validate.jsp?userId=" + trim(field.value) + "&time=" + new Date().getTime();

xmlHttp.open("GET",url,true);

xmlHttp.onreadystatechange = function(){

//alert(xmlHttp.readyState);

if(xmlHttp.readyState ==4){

if (xmlHttp.readyState == 4) {

//HTTP协议状态为成功

if (xmlHttp.status == 200) {

if (trim(xmlHttp.responseText) != "") {

//alert(xmlHttp.responseText);

//document.getElementById("userIdSpan").innerHTML = "<font color='red'>            " + xmlHttp.responseText + "</font>"

generateInnerHTML("userIdSpan",xmlHttp.responseText);

}else {

//document.getElementById("userIdSpan").innerHTML = "";

generateInnerHTML("userIdSpan","");

}

}else {

alert("请求失败，错误码=" + xmlHttp.status);

}

};

xmlHttp.send(null);