$.ajax( { async : false } ) request is still firing asynchronously?

问题:

I got a little problem here guys. I'm trying to implement the following scenario:

1. A user opens the home page and sees a list of other users and clicks to add one to his friend list.
2. I issue an Ajax request to a server resource to validate if the user is logged in, if so, I issue another ajax request to another server resource to actually add it to the user's friend list.

Sounds simple? Here's what I've done: I created a function isLoggedIn that will issue the first request to the server in order to determine if the user is logged in. I issue this request using jQuery.ajax method. Here's my function looks like:

function isLoggedIn() {      $.ajax({     async: "false",         type: "GET",         contentType: "application/json; charset=utf-8",         dataType: "json",         url: "/isloggedin",         success: function(jsonData) {             alert("jsonData =" + jsonData.LoggedIn);             return jsonData.LoggedIn;         }     }); } 

The returned JSON is very simple, it looks like the following:

{ LoggedIn: true } or { LoggedIn : false }  

Now this method, actually works and displays the alert correctly: JsonData = true if logged in, and JsonData = false if not logged in. Up to this point there's no problem, the problem occurs when I try to call this method: I call it like so:

$(".friend_set .img").click(function() {     debugger;     if (isLoggedIn()) {           alert("alredy logged in");         trackAsync();         popupNum = 6;     }     else {         alert("not logged in"); //always displays this message.         popupNum = 1;     }     //centering with css      centerPopup(popupNum);     //load popup     loadPopup(popupNum);     return false;  }); 

Calling isLoggedIn always returns false, and it returns false before the ajax request finishes (because the messagejsonData = trueis displayed after the message "not logged in". I made sure that the request is **NOT** Asynchronous by statingasync: false`!

Apparently it's still working asynchronously, though. What am I missing here guys?

回答1:

You need async:false, not async:"false". (i.e. pass boolean false, not string "false").

Edit: also with async requests you need to return a value after the call to ajax, not inside your success handler:

function isLoggedIn() {     var isLoggedIn;     $.ajax({         async: false,         // ...         success: function(jsonData) {             isLoggedIn = jsonData.LoggedIn         }     });     return isLoggedIn  } 

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