Question

Can jQuery provide a fallback for failed AJAX calls? This is my try:

function update() {
    var requestOK = false;

    $.getJSON(url, function(){
        alert( request successful );
        requestOK = true;
    });

    if (!requestOK) {
        alert( request failed );
    }
}

Unfortunately, even if the callback function of the $.getJSON() method is called, i get the message request failed , before the callback function has the opportunity to set the requestOK variable. I think it s because the code runs in parallel. Is there a way to handle such situations? I thought about chaining or some way of waiting for the AJAX request, including its callback function. But how? Does anyone know how to do that?

Answer 1

You will need to either use the lower level $.ajax call, or the ajaxError function. Here it is with the $.ajax method:

function update() {
  $.ajax({
    type:  GET ,
    dataType:  json ,
    url: url,
    timeout: 5000,
    success: function(data, textStatus ){
       alert( request successful );
    },
    fail: function(xhr, textStatus, errorThrown){
       alert( request failed );
    }
  });
}

EDIT I added a timeout to the $.ajax call and set it to five seconds.

Answer 2

Dougs answer is correct, but you actually can use $.getJSON and catch errors (not having to use $.ajax). Just chain the getJSON call with a call to the fail function:

$.getJSON( /foo/bar.json )
    .done(function() { alert( request successful ); })
    .fail(function() { alert( request failed ); });

Live demo: http://jsfiddle.net/NLDYf/5/

This behavior is part of the jQuery.Deferred interface.
Basically it allows you to attach events to an asynchronous action after you call that action, which means you don t have to pass the event function to the action.

Read more about jQuery.Deferred here: http://api.jquery.com/category/deferred-object/

Answer 3

Yes, it s built in to jQuery. See the docs at jquery documentation.

ajaxError may be what you want.

Answer 4

I prefer to this approach because you can return the promise and use .then(successFunction, failFunction); anywhere you need to.

var promise = $.ajax({
    type:  GET ,
    dataType:  json ,
    url: url,
    timeout: 5000
  }).then(function( data, textStatus, jqXHR ) {
    alert( request successful );
  }, function( jqXHR, textStatus, errorThrown ) {
    alert( request failed );
});

//also access the success and fail using variable
promise.then(successFunction, failFunction);

Answer 5

I believe that what you are looking for is error option for the jquery ajax object

getJSON is a wrapper to the $.ajax object, but it doesn t provide you with access to the error option.

EDIT: dcneiner has given a good example of the code you would need to use. (Even before I could post my reply)

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