Question

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How can I get jQuery to perform a synchronous, rather than asynchronous, AJAX request?
how to wait for an ajax call to return

Hear me out. I completely understand this code segment.

$.getJSON(someURL, function(data){
    //do something with my data
})
.success(function () {
    //Call what you want on success
})

This seems fine if I just need to take one action that is pretty static. However, what if I want to be less restricted, for instance this

function my_func(){
    $.getJSON(someURL, function(data){
        //do something with my data... like modify an array or the dom
    })
}

Now the driver

my_func();
//Now I want to call a function that relies on the data that my_func brought into the script.

Is there something wrong with the way I’m coding my script if I want to do it like this? Or am I just missing some awesome built in method?

Answer 1

I see two possible jQuery-ish ways there.

The first would be to use another callback that can be passed to my_func:

function my_func(callback) {
    $.getJSON(someUrl, function(data) {
        // ...do stuff ...
        if ($.isFunction(callback)) { callback(data); }
    });
}

my_func(function(data) {
    // ..do more stuff..
});

The second way would be to create a custom event that gets triggered inside my_func and can be listened to from the outside:

function my_func() {
    $.getJSON(someUrl, function(data) {
        $(document).triggerHandler('my_func:data-received', [data]);
    });
}

$(document).on('my_func:data-received', function(event, data) {
    // ...do stuff...
});

my_func();

I strongly recommend using async: false only if it is absolutely necessary.

---

Just another (very neat) way to deal with this is the jQuery.Deferred object:

function my_func() {
    var d = new $.Deferred();
    $.getJSON(someUrl, function(data) {
        d.resolve(data);
    });
    return d;
}

my_func().done(function(data) {
    // ...do stuff...
});

Your function returns an object that allows to register callbacks. Within the function you then just need to make sure to call resolve to invoke all registered done callback handlers.