Perform asynchronous call before calling function

Question

I have a function, authenticate() that uses $post() to retrieve a session key from my server. I believe $post is an asynchronous call. Whenever I perform any action in my script, I want to ensure that I have a sessionKey, and if I do not have a sessionKey I want to authenticate(). My problem is how do I run performTask() after I have called authenicate()?

function foo() {
    if (sessionKey) {
        performTask();
    } else {
        authenciate();
        performTask();
    }
}

function authenticate() {       
    $.post(url, function(data) {
        sessionKey = data.sessionKey;
    });
}

EDIT: I also do not want to put in authenticate()'s callback function performTask() as authenticate() will be called from several different functions.

Check the simplified update. You can make the caller just add a small bit to it for every authenticated call. — Meligy, Feb 29 '12 at 05:52

score 2 · Answer 1 · answered Feb 29 '12 at 03:45

Pass the callback to authenticate() itself using jQuery's Promise interface (see documentation):

function authenticate(callback) {
    var rq = $.post(url, function(data) {
        sessionKey = data.sessionKey;
    });

    if(callback) {
        rq.success(callback);
    }
}

Now just call authenticate(performTask), for example.

score 1 · Accepted Answer · edited Feb 29 '12 at 04:00

1

You can pass in a callback to the authenticate method. If authenticate is called from 20 different places, you can pass in 20 different callback methods.

function foo() {
    if (sessionKey) {
        performTask();
    } else {
        authenciate(function() {
           performTask();
        });
    }
}

function authenticate(callback) {       
    $.post(url, function(data) {
        sessionKey = data.sessionKey;
        if (callback) callback();
    });
}

edited Feb 29 '12 at 04:00

josh3736

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answered Feb 29 '12 at 03:48

CodeThug

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@icu222much: This answer is on the right track, but it's missing one important piece that @minitech's answer has -- checking that a callback was passed to `authenticate` before trying to invoke it. (`if (callback) callback();`) Otherwise, simply calling `authenticate();` (without a callback) will throw a `ReferenceError` . I've taken the liberty of adding the appropriate check. – josh3736 Feb 29 '12 at 03:58

score 0 · Answer 3 · answered Feb 29 '12 at 03:44

JQuery's AJAX calls have callback functions (success and error). You can pass in the after-authentication action as the callback to do it after authentication has completed.

Alternately, you can set am option to make the calls synchronous.

Sorry for not linking to the documentation; I'm posting from my phone. Just google "jquery.ajax" to find the documentation.

*EDIT:*As a response to your edit, you could give your authenticate method a parameter to use as a callback function if you want to change what happens after the call (or do nothing) on a case-by- case basis.

score 0 · Answer 4 · edited May 23 '17 at 12:03

Check this question: How can I get jQuery to perform a synchronous, rather than asynchronous, Ajax request?

It has an example of doing AJAX synchronously. Basically you pass an async:false param, and might require using the ajax() method instead of the post() shortcut to it.

Update:

Another thing you can do is wrap the whole thing in a function like:

function foo() {
    authenciate(function() {
       performTask();
    });
}

function authenticate(callback) {     

    if (!callback) { return; }

    if (sessionKey) {
        callback();
    } else {
        $.post(url, function(data) {
            sessionKey = data.sessionKey;
            callback();
        });
    }
}

-1; [**never** use synchronous AJAX calls](http://stackoverflow.com/a/7337091/201952). — josh3736, Feb 29 '12 at 03:47

Perform asynchronous call before calling function

4 Answers4