getJSON return variable.. solution?

Question

My function fetches if the user is banned and i want to return a variable that determines if a popup displays; but as I've found out you can't return a variable from a getJSON function.

 function fetchban() {
    $.getJSON('/fetchban.php',function(data) {

        if(data==0) {

            var banned =  data;
        } else {
            $.each(data,function(index,result) {
            $('#ban-prompt').html(result);
            $('.popup-background').show();
            $('#ban-container-2').show();
            });
        }

    });

    return banned;
}

$('.button').click(function() {
var banned = fetchban();

if(banned==0) {

//display-popup

}

});

There are alot of lines i call the fetchban function, so i would prefer the getJSON in a function. What is the solution?

possible duplicate of jQuery getJSON - Return value to the caller function — Denys Séguret
– Denys Séguret, Commented Jul 20, 2012 at 12:10
or just set the banned flag inside the JSON, like {banned:"false",datas:{... your regular object}} and then go var banned = data.banned — Carlo Moretti
– Carlo Moretti, Commented Jul 20, 2012 at 12:10
That's one of the most duplicated question on SO. Just have to look at the right column to see some of the usual answers. — Denys Séguret
– Denys Séguret, Commented Jul 20, 2012 at 12:10

T.J. Crowder · Accepted Answer · 2012-07-20 12:10:09Z

3

There are two problems with your function.

The first, and the most significant, is that it assumes that getJSON is synchronous. It is asynchronous by default, meaning it's impossible for fetchban to return a value based on the data retrieved. Instead, fetchban should accept a callback it calls with the result.

The second (which will go away anyway once you fix the first), is that you're trying to return a variable from fetchban that isn't declared (because you declare it inside your getJSON success handler).

So you'd change fetchban to look something like:

function fetchban(callback) {
    $.getJSON('/fetchban.php',function(data) {
        var banned;

        // ...figure out what `banned` should be from the `data`,
        // I'm afraid I couldn't make sense of the code, looked
        // like it always set `banned` to 0.

        // Call the callback with the result
        callback(banned);
    });
}

And then instead of:

$('.button').click(function() {
    var banned = fetchban();

    if(banned==0) {
        //display-popup
    }
});

do this:

$('.button').click(function() {
    fetchban(function(banned) {
        if(banned==0) {
            //display-popup
        }
    });
});

...or much better, fetch it earlier so you already have that information when the click arrives. Users don't like delays when they click, and even the best case on a web round-trip is noticeable to human beings.

answered Jul 20, 2012 at 12:10

T.J. Crowder

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2 Comments

user892134 Over a year ago

How do i do "fetchban should accept a callback it calls with the result"?

T.J. Crowder Over a year ago

@user892134: See update. Or any of about 757,521 callback tutorials and examples on the web. ;-)

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