JSONP request returning error: “Uncaught SyntaxErr

问题:

So I'm trying to make a request to the Stack Exchange API with the following jQuery code:

$.ajax({                                                                                                                                                                                                        
    type: 'POST',                                                                                                                                                                                                 
    url: 'http://api.stackoverflow.com/1.1/stats',                                                                                                                                              
    dataType: 'jsonp',                                                                                                                                                                                                
    success: function() { console.log('Success!'); },                                                                                                                                                                                       
    error: function() { console.log('Uh Oh!'); }                                                                                                                                                              
});   

But when I open the file on my machine, in either FireFox or Chrome, and make the request, I get this error:

Resource interpreted as Script but transferred with MIME type application/json.
Uncaught SyntaxError: Unexpected token :
Uh Oh!

I don't have a clue what's going on. I know the Stack Exchange API Gzips its responses, would this cause any trouble?

回答1:

You have to set an unconventional parameter to get the SO API to work. Rather than the conventional callback, you need to pass a jsonp parameter.

Furthermore, you can't do POST with JSONP.

$.ajax({                                                                                                                                                                                                        
    type: 'GET',                                                                                                                                                                                                 
    url: 'http://api.stackoverflow.com/1.1/stats',                                                                                                                                              
    dataType: 'jsonp',                                                                                                                                                                                                
    success: function() { console.log('Success!'); },                                                                                                                                                                                       
    error: function() { console.log('Uh Oh!'); },
    jsonp: 'jsonp'                                                                                                                                                
});

---

It is not possible to do cross-domain AJAX using the conventional XMLHTTPRequest. This is for security reasons (it's call the same-origin policy).

There is a workaround. script tags are not subject to this restriction. This means that you can insert a script tag into the document that calls a URL. If you define a globally-accessible function in your script and tell the remote server what that function is called, the server can pass code that wraps the data to be sent in a call to that function.

The difficulty you had here is with the StackOverflow API. Conventionally, you would use the callback argument in your request, to tell the server what your function is called. However, StackOverflow's API asks you to use the jsonp parameter instead.

回答2:

Try this URL: http://api.stackoverflow.com/1.1/stats?jsonp=callme

"callme" is the name of your callback function - in your GLOBAL NAMESPACE (window object).

By the way, if you are running Firefox and have the JSONView add-on installed you can test the above URL (and yours for comparison) directly.

Result from calling the URL:

callme({
  "statistics": [
...
  ]
})