解决ajax异步传输数据，return返回为undefined的问题

 

function GetUserInfo(tp) {
    var username;
    $.ajax({
        type: "POST",
        cache: false,
        data: "type=exlogin&tp=" + tp,
        url: "Handle/OpeartionHandler.ashx",
        success: function(userinfo) {
            username = userinfo;
        }, error: function(data) {
            username = "";
        }
    });
    return username;
}

function GetUserInfo(tp) {
    var username;
    $.ajax({
        type: "POST",
        cache: false,
        data: "type=exlogin&tp=" + tp,
        url: "Handle/OpeartionHandler.ashx",
        success: function(userinfo) {
            username = userinfo;
        }, error: function(data) {
            username = "";
        }
    });
    return username;
}

对于此方法调用之后会一直返回undefined，原因是Jquery的ajax是异步的，所以大多时候没执行完AJAX就return htmlcontent了，所以会一直返回undefined,

解决方法：添加async: false,即修改此方法为同步

function GetUserInfo(tp) {
    var username;
    $.ajax({
        type: "POST",
        cache: false,
        data: "type=exlogin&tp=" + tp,
        async: false,
        url: "Handle/OpeartionHandler.ashx",
        success: function(userinfo) {
            username = userinfo;
        }, error: function(data) {
            username = "";
        }
    });
    return username;
}