Javascript 返回对象的Ajax JS函数未定义

我有一个返回JS对象的AJAX函数。然而，当我给函数赋值时，我得到了未定义的变量。在FireBug中调试时，一切正常，但我尝试将结果分配给var测试仪时除外

这是我的密码

    function AllBidData(HighestBid,MinimumBid,HighestProxyBid) {
        return {
            HighestBid: HighestBid,
            MinimumBid: MinimumBid,
            HighestProxyBid: HighestProxyBid
        };
    }



    function GetAllBidData() {          

        $.ajax({
            type: "POST",
            dataType: "json",
            url: "/VehicleAuction/GetAllBidData",
            data: { AuctionID: AuctionID, UserID: UserID }

        }).done(function (msg) {

            var BidDate = new AllBidData(msg.HighestBid, msg.MinimumBid, msg.HighestProxyBid);
            return BidDate;
        });
    }    

var tester = GetAllBidData(); 
//why is tester is undefined?

更新和解决方案-这就是我解决这个问题的方法-使用延迟对象

function GetAllBidData() {          
    return $.ajax({
        type: "POST",
        dataType: "json",
        url: "/VehicleAuction/GetAllBidData",
        data: { AuctionID: AuctionID, UserID: UserID }
    });
}

function AllBidData(data) {
    return {
        HighestBid: data.HighestBid,
        MinimumBid: data.MinimumBid,
        HighestProxyBid: data.HighestProxyBid
    };
}

var tester = null;
tester = GetAllBidData().done(AllBidData);

---

这是异步调用。函数在ajax调用发生之前执行并返回值

function GetAllBidData(callback) {          

        $.ajax({
            type: "POST",
            dataType: "json",
            url: "/VehicleAuction/GetAllBidData",
            data: { AuctionID: AuctionID, UserID: UserID }

        }).done(function (msg) {

            var BidDate = new AllBidData(msg.HighestBid, msg.MinimumBid, msg.HighestProxyBid);
            callback(BidDate);
        });
    }    

var tester = GetAllBidData(function(yourValue){
    //do stuff here with yourValue
});