[jQuery.ajax about jsonp] error description for dataType and more explicit description for url

[Aqours]

URL: http://api.jquery.com/jQuery.ajax/

1. An error description for dataType
   
   Actually cross-domain "json" requests will be not converted to "jsonp".
2. JavaScript code

// the url of current page is
// http://www.a.com
// then send a request
// http://www.b.com/search.php support jsonp
$.ajax({
    url: "http://www.b.com/search.php?callback=?",
    data: {
        // ...
    },
    dataType: "json"
});

This request will be auto converted to "jsonp". Write this feature on jQuery document that will be good for users. I think this way is more useful than dataType: "jsonp" occasionally.

[dmethvin]

Doesn't your example show the documentation is correct?

[Aqours]

1. The wrong on jQuery document.
2. Adds an extra "?callback=?" to the end of your URL to indicate that loads in a JSON block using JSONP when using dataType: "json" or dataType: "jsonp". (I think it will be a more accurate description about my example)

[onebytegone]

I recently noted this issue as well. The section that is particularly confusing is listed below, please note bold italicized text.

"json": Evaluates the response as JSON and returns a JavaScript object. Cross-domain "json" requests are converted to "jsonp" unless the request includes jsonp: false in its request options. The JSON data is parsed in a strict manner; any malformed JSON is rejected and a parse error is thrown. As of jQuery 1.9, an empty response is also rejected; the server should return a response of null or {} instead. (See json.org for more information on proper JSON formatting.)

From this section of the docs I would gather that, using the example that @Aqours gave, the following would result:

1. The script loads on the domain of 'https://www.a.com' in a browser does not have CORS, e.g. IE9.

2. An ajax request is made to a different domain using the json data type.

   $.ajax({
      url: 'https://www.b.com/search.php',
      dataType: 'json'
   });

3. jQuery appends a callback parameter to the url and makes the call via the script transport

   • This assumption is based on the following:
     • The request is cross domain ('https://www.b.com' !== 'https://www.a.com')
     • 'jsonp' !== false as the jsonp option defaults to callback
     • The dataType is json and according to "Cross-domain "json" requests are converted to "jsonp"" will be treated as JSONP

The above however does not occur, no callback is appended nor is the <script> transport used. In order for the request to be treated as JSONP, that of the url receiving a callback function and being request via the script tag transport, one of the following must happen:

// Option 1: `callback=?` in url
$.ajax({
   url: 'https://www.b.com/search.php?callback=?',
   dataType: 'json'
});

// Option 2: `dataType` set to `jsonp`
$.ajax({
   url: 'https://www.b.com/search.php',
   dataType: 'jsonp'
});

In light of this, the following seems more accurate:

"json": Evaluates the response as JSON and returns a JavaScript object. Cross-domain "json" requests that have a callback placeholder, e.g. ?callback=?, are performed using JSONP unless the request includes jsonp: false in its request options. The JSON data is parsed in a strict manner; any malformed JSON is rejected and a parse error is thrown. As of jQuery 1.9, an empty response is also rejected; the server should return a response of null or {} instead. (See json.org for more information on proper JSON formatting.)

A more extensive set of examples of this behavior can be found at: https://github.com/onebytegone/jquery-ajax-jsonp

Note: This behavior has been confirmed in jQuery v1.11.0, v1.12.4, v2.2.4, and v3.1.1.

[dmethvin]

This sounds like a very good clarification, can you submit a PR at https://github.com/jquery/api.jquery.com/?

The current docs are consistent in that dataType is about the type of the received data and it only mentions changing the URL when it does so itself. However, I can understand the confusion.

[AurelioDeRosa]

@dmethvin are you sure you wanted to close this issue?

[dmethvin]

Duh, no! I must have confused two tabs at the time. @onebytegone you are in the right place! 😕

[mgol]

@Aqours Why did you close it? Reopening.

[Aqours]

@mgol For a long time no one had dealt with this issue. Remain issue opened if you track it.

[mgol]

@Aqours All of the people working on this repo are volunteers and we have limited manpower so there are silent periods.