用于验证用户名是否可用的php ajax实现代码

//初始化、指定处理函数、发送请求的函数

//var poststr = "act=reply&bookid="+bookid+"&book_content="+ book_content;
//type:post or get
function send_request(http_request,url,poststr) {
    // 确定发送请求的方式和url以及是否同步执行下段代码
    http_request.open("post", url, true);
    http_request.setrequestheader("content-type","application/x-www-form-urlencoded");
    http_request.send(poststr);
}

//创建对象 兼容多浏览xmlhttp创建方法

function create_obj(){
    var http_request = false;

    //开始初始化xmlhttprequest对象
    if(window.xmlhttprequest) { //mozilla 浏览器
        http_request = new xmlhttprequest();
        if (http_request.overridemimetype) {//设置mime类别
            http_request.overridemimetype("text/xml");
        }
    }
    else if (window.activexobject) { // ie浏览器
        try {
            http_request = new activexobject("msxml2.xmlhttp");
        } catch (e) {
            try {
                http_request = new activexobject("microsoft.xmlhttp");
            } catch (e) {}
        }
    }

    if (!http_request) { // 异常，创建对象实例失败
        return false;
    }

    return http_request;
}

//这段代码是获取username值，发送到服务器端由php查询数据返回一个ture false验证用户名是否可用。

function getcheck(){
    var http_request = create_obj();
    http_request.onreadystatechange = function(){
        if (http_request.readystate == 4) {
            if (http_request.status == 200) {
    var http_result2 = http_request.responsetext;
    if('该登录名可以使用'==http_result2){
     cancel_popup_win('username',true);
     username_check = true;
    }else{
        popup_win('username',http_result2);
        username_check = false;
    }
            }
        }
    }
    var username=document.getelementbyid('username').value;
    var poststr = "act=check&userid="+ username;
    send_request(http_request,"http://www.3ppt.com",poststr);
}
  
</script>

调用方法相对简单

<li>
<span class="dlm"><em>设置登录名：</em>
      <input tabindex="1" class="text_2" name="username" id="username" value="" type="text" maxlength="16"  autocomplete="off"  onblur="getcheck();"/>登录名:4-16/怪字符/全数字/无内容/下划线/有全角/有空格/有大写/有汉字< /span>
    </li>