无法使用JSONP获取远程JSON

Question

I'm trying to retrieve a remote JSON using jQuery 1.11.1. The remote server does support jsonp and I'm able to download the .jsonp file by simply entering the call address and ?callback=foo in a browser.

However, when I try to get it using ajax, it fails.

$.ajax({
    type: "GET",
    url: "http://path-to-remote-server.net/file.jsonp",
    dataType: 'jsonp',
    jsonp : "callback",
    jsonpCallback: "e",
    success: function(r) {
        console.log(r);
    }
});

A quick look at the console tells me that it's a bad request, probably because it seems that jQuery passes a second unwanted parameter, making the request look like this :

http://path-to-remote-server.net/file.jsonp?callback=e&_=1406722474006

This happens even when I omit the jsonp and jsonpCallback options. The request then looks like this :

http://path-to-remote-server.net/file.jsonp?callback=jQuery111106199050471186638_1406722685544&_=1406722685545

Using the short cut $.getJSON doesn't work either, but not for the same reason it seems :

$.getJSON("http://path-to-remote-server.net/file.jsonp?callback=e", function(r){
    console.log(r);
});

This doesn't trigger any error in the console, but nothing gets logged either, as if it didn't get anything back from the server.

Why is that, and how can I avoid it?

Thank you all in advance!

Answer 1

From the manual :

cache (default: true, false for dataType 'script' and 'jsonp')
Type: Boolean
If set to false, it will force requested pages not to be cached by the browser. Note: Setting cache to false will only work correctly with HEAD and GET requests. It works by appending "_={timestamp}" to the GET parameters. The parameter is not needed for other types of requests, except in IE8 when a POST is made to a URL that has already been requested by a GET.

So add cache: true to your Ajax parameters.

Answer 2

The last query string argument automatically added by jQuery is needed to avoid browser caching. Otherwise if you do the same JSONP call in the same or in any other page of your site, you will get the cached result instead of the fresh one. So if your server does support JSONP it should accept such requests.

It seems to be a server-side issue, so you should check what is going on there :)