使用JSONP时，如何捕获jQuery $ .getJSON（或$ .ajax，数据类型设置为'jsonp'）错误？

Question

Is it possible to catch an error when using JSONP with jQuery? I've tried both the $.getJSON and $.ajax methods but neither will catch the 404 error I'm testing. Here is what I've tried (keep in mind that these all work successfully, but I want to handle the case when it fails):

jQuery.ajax({
    type: "GET",
    url: handlerURL,
    dataType: "jsonp",
    success: function(results){
        alert("Success!");
    },
    error: function(XMLHttpRequest, textStatus, errorThrown){
        alert("Error");
    }
});

And also:

jQuery.getJSON(handlerURL + "&callback=?", 
    function(jsonResult){
        alert("Success!");
    });

I've also tried adding the $.ajaxError but that didn't work either:

jQuery(document).ajaxError(function(event, request, settings){
   alert("Error");
});

Thanks in advance for any replies!

Answer 1

Here 's my extensive answer to a similar question.

Here's the code:

jQuery.getJSON(handlerURL + "&callback=?", 
    function(jsonResult){
        alert("Success!");
    })
.done(function() { alert('getJSON request succeeded!'); })
.fail(function(jqXHR, textStatus, errorThrown) { alert('getJSON request failed! ' + textStatus); })
.always(function() { alert('getJSON request ended!'); });

Answer 2

It seems that JSONP requests that don't return a successful result never trigger any event, success or failure, and for better or worse that's apparently by design.

After searching their bug tracker, there's a patch which may be a possible solution using a timeout callback. See bug report #3442 . If you can't capture the error, you can at least timeout after waiting a reasonable amount of time for success.

Answer 3

Detecting JSONP problems

If you don't want to download a dependency, you can detect the error state yourself. It's easy.

You will only be able to detect JSONP errors by using some sort of timeout. If there's no valid response in a certain time, then assume an error. The error could be basically anything, though.

Here's a simple way to go about checking for errors. Just use a success flag:

var success = false;

$.getJSON(url, function(json) {
    success = true;
    // ... whatever else your callback needs to do ...
});

// Set a 5-second (or however long you want) timeout to check for errors
setTimeout(function() {
    if (!success)
    {
        // Handle error accordingly
        alert("Houston, we have a problem.");
    }
}, 5000);

As thedawnrider mentioned in comments, you could also use clearTimeout instead:

var errorTimeout = setTimeout(function() {
    if (!success)
    {
        // Handle error accordingly
        alert("Houston, we have a problem.");
    }
}, 5000);

$.getJSON(url, function(json) {
    clearTimeout(errorTimeout);
    // ... whatever else your callback needs to do ...
});

Why? Read on...

---

Here's how JSONP works in a nutshell:

JSONP doesn't use XMLHttpRequest like regular AJAX requests. Instead, it injects a <script> tag into the page, where the "src" attribute is the URL of the request. The content of the response is wrapped in a Javascript function which is then executed when downloaded.

For example.

JSONP request: https://api.site.com/endpoint?this=that&callback=myFunc

Javascript will inject this script tag into the DOM:

<script src="https://api.site.com/endpoint?this=that&callback=myFunc"></script>

What happens when a <script> tag is added to the DOM? Obviously, it gets executed.

So suppose the response to this query yielded a JSON result like:

{"answer":42}

To the browser, that's the same thing as a script's source, so it gets executed. But what happens when you execute this:

<script>{"answer":42}</script>

Well, nothing. It's just an object. It doesn't get stored, saved, and nothing happens.

This is why JSONP requests wrap their results in a function. The server, which must support JSONP serialization, sees the callback parameter you specified, and returns this instead:

myFunc({"answer":42})

Then this gets executed instead:

<script>myFunc({"answer":42})</script>

... which is much more useful. Somewhere in your code is, in this case, a global function called myFunc :

myFunc(data)
{
    alert("The answer to life, the universe, and everything is: " + data.answer);
}

That's it. That's the "magic" of JSONP. Then to build in a timeout check is very simple, like shown above. Make the request and immediately after, start a timeout. After X seconds, if your flag still hasn't been set, then the request timed out.

Answer 4

I know this question is a little old but I didn't see an answer that gives a simple solution to the problem so I figured I would share my 'simple' solution.

$.getJSON("example.json", function() {
      console.log( "success" );
}).fail(function() { 
      console.log( "error" ); 
}); 

We can simply use the .fail() callback to check to see if an error occurred.

Hope this helps :)

Answer 5

If you collaborate with the provider, you could send another query string parameter being the function to callback when there's an error.

?callback=?&error=?

This is called JSONPE but it's not at all a defacto standard.

The provider then passes information to the error function to help you diagnose.

Doesn't help with comm errors though - jQuery would have to be updated to also callback the error function on timeout, as in Adam Bellaire's answer.

Answer 6

Seems like this is working now:

jQuery(document).ajaxError(function(event, request, settings){
   alert("Error");
});

Answer 7

I use this to catch an JSON error

try {
   $.getJSON(ajaxURL,callback).ajaxError();
} catch(err) {
   alert("wow");
   alert("Error : "+ err);
}

Edit: Alternatively you can get the error message also. This will let you know what the error is exactly. Try following syntax in catch block

alert("Error : " + err);

Answer 8

Mayby this works?

.complete(function(response, status) {
    if (response.status == "404")
        alert("404 Error");
    else{
        //Do something
    }   
    if(status == "error")
        alert("Error");
    else{
        //Do something
    }
});

I dont know whenever the status goes in "error" mode. But i tested it with 404 and it responded

Answer 9

you ca explicitly handle any error number by adding this attribute in the ajax request:

statusCode: {
        404: function() {
          alert("page not found");
        }
    }

so, your code should be like this:

jQuery.ajax({
type: "GET",
statusCode: {
        404: function() {
          alert("page not found");
        }
},
url: handlerURL,
dataType: "jsonp",
success: function(results){
    alert("Success!");
},
error: function(XMLHttpRequest, textStatus, errorThrown){
    alert("Error");
}
});

hope this helps you :)

Answer 10

I also posted this answer in stack overflow - Error handling in getJSON calls

I know it's been a while since someone answerd here and the poster probably already got his answer either from here or from somewhere else. I do however think that this post will help anyone looking for a way to keep track of errors and timeouts while doing getJSON requests. Therefore below my answer to the question

The getJSON structure is as follows (found on http://api.jqueri.com ):

$(selector).getJSON(url,data,success(data,status,xhr))

most people implement that using

$.getJSON(url, datatosend, function(data){
    //do something with the data
});

where they use the url var to provide a link to the JSON data, the datatosend as a place to add the "?callback=?" and other variables that have to be send to get the correct JSON data returned, and the success funcion as a function for processing the data.

You can however add the status and xhr variables in your success function. The status variable contains one of the following strings : "success", "notmodified", "error", "timeout", or "parsererror", and the xhr variable contains the returned XMLHttpRequest object ( found on w3schools )

$.getJSON(url, datatosend, function(data, status, xhr){
    if (status == "success"){
        //do something with the data
    }else if (status == "timeout"){
        alert("Something is wrong with the connection");
    }else if (status == "error" || status == "parsererror" ){
        alert("An error occured");
    }else{
        alert("datatosend did not change");
    }         
});

This way it is easy to keep track of timeouts and errors without having to implement a custom timeout tracker that is started once a request is done.

Hope this helps someone still looking for an answer to this question.