刷新后 JavaScript 未按顺序运行

Question

我有一个系统，通过检查用户是否登录、抓取匹配的用户药物条目，然后使用它来将消息标记为已读/未读。从一个 View 切换到另一个 View 时它工作正常，但有时当我刷新时，它会首先运行显示代码(具有空 dateLastSeen)，然后运行从数据库获取信息的代码(通过调试检查)。下面是按 View 中的顺序排列的代码:

<script type="text/javascript">
    // If user isn't logged in, hide submission/ignore drug visits
    // Otherwise, continue to else statement and figure out drug visit stuff
    var userLoggedIn = @Html.Raw(Json.Encode(ViewData["Username"])) + '';
    var dateLastSeen = null;
    if (userLoggedIn == "Guest") {
        $('.expandMessagePost').hide();
    }
    // If they're logged in but no pairing of user/NDC exists, set all messages to unread
    // If they're logged in and have visited the page, compare the date in the DrugVisit entry
    // and compare that to the message dates, and if they're newer, set them to unread
    else {
        $.getJSON("/api/DrugVisit", function (drugVisitsJsonPayload) {
            $(drugVisitsJsonPayload).each(function (i, item) {
                // Page has been visited
                if (item.NDC == '@Model.Item1.NDC' && item.Username == userLoggedIn) {
                    dateLastSeen = item.Date;
                    console.log("Date found!");
                }
            });
        });
    }

    $.getJSON("/api/Message/", function (messagesJsonPayload) {
        $(messagesJsonPayload).each(function (i, item) {
            if (item.NDC == '@Model.Item1.NDC') {
                var badge = "";
                // Check (if user logged in) if unread, update DrugVisit entry
                if (userLoggedIn != "Guest") {
                    if (dateLastSeen != null) {
                        if (item.Date > dateLastSeen) {
                            badge = "[UNREAD] - ";
                            console.log(dateLastSeen + " - " + item.Date);
                        }
                    }
                    else {
                        badge = "[UNREAD] - ";
                        console.log(dateLastSeen + " - " + "NULL WTF");
                    }
                }
                $("#messageListing").append('<li> \
                                            ' + badge + item.User + ' - ' + formatDateForOutput(item.Date) + ' - ' + item.Text + ' \
                                             </li>');
            }
        }
        );
    }
    );
</script>

这是某种竞争条件吗？我对 MVC 和 ASP.net 还很陌生，所以我不知道在这里做什么。感谢您的帮助。

Answer 1

我不太明白您希望事情发生的顺序，但您可能应该使用 getJson 调用中的 .complete 函数 - 例如，如果您想做 $.getJSON("/api/DrugVisit" 然后，一旦您获得了数据，就执行 $.getJSON("/api/Message/"，您应该执行类似的操作:

$.getJSON("/api/DrugVisit", function (drugVisitsJsonPayload) {
   //do stuff
}).complete(function() {
   $.getJSON("/api/Message/", function (messagesJsonPayload) {
     //do more stuff, knowing that the first call is finished
   });
});