Question

43

JSONP Callback function

rated 0 times [ 49] [ 6] / answers: 1 / hits: 32546 / 11 Years ago, fri, april 19, 2013, 12:00:00

I was looking into the concept of JSONP callback function. I read some articles regarding that and wanted to get a good grasp of the concept of JSONP.

So, I uploaded one json file to the server - json file

And here is the js code which I wrote to retrieve the data. The call is made from localhost to the abhishekprakash.com.

var xhr;

var dataList;

xhr = new XMLHttpRequest();



xhr.open('GET', 'http://abhishekprakash.com/script/example.json?callback=func_callbk',  true);

xhr.send();



func_callback = function(data){

    alert(data.data.people[0].id);

}



xhr.onreadystatechange = function(){

if(xhr.readyState == 4){

            console.log(dataList);

    }

};

And this is the response that I get in the console:

snap

The callback function is called but it does not contain the Json data.
What am I missing?

Any help is appreciated.

Thanks

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zoey

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3 Years ago

answered 11 Years ago timothyc · Accepted Answer

That example service returns JSON, not JSONP.

The point of JSONP is that due to Same Origin Policy security restrictions, Javascript from domain A cannot make a GET request to resources on domain B; in other words a script cannot retrieve data cross-domain.

JSONP solves this by making domain B explicitly cooperate in the cross-domain data sharing. The script from domain A specifies the name of a callback function and embeds the URL of domain B in the document as if it were including a regular external Javascript file. Domain B then outputs data like this:

callbackFuncName({ data : foo, ... });

That means domain B explicitly outputs a Javascript snippet which calls the specified callback function with the data.

So, unless domain B explicitly cooperates in this, you cannot simply get a JSONP response from it.