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Asked: 2026-05-28T18:31:00+00:00

I need to parse JSONP messages in .NET and find JSON in those messages.

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I need to parse JSONP messages in .NET and find JSON in those messages. Is there any up to date specification describing a valid JSONP message?

I found this blog post (from 2005) by Bob Ippolito specifying the first JSONP proposal, where a JSONP message could contain almost any JavaScript code.

I also found a probably more recent specification on json-p.org allowing only function calls to functions specified in a requesting URI parameter named callback.

Finally Wikipedia says:

While the padding (prefix) is typically the name of a callback
function that is defined within the execution context of the browser,
it may also be a variable assignment, an if statement, or any other
JavaScript statement. The response to a JSONP request (namely, a
request following the JSONP usage pattern) is not JSON and is not
parsed as JSON; the returned payload can be any arbitrary JavaScript
expression, and it does not need to include any JSON at all. But
conventionally, it is a JavaScript fragment that invokes a function
call on some JSON-formatted data.

So is there any global definition what makes a valid JSONP response and what JavaScript constructs are allowed? Should I expect any JavaScript code, because that is what current browsers accept (because it has application/javascript content type)?

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1 Answer

  1. Editorial Team

    As JSONP is a pattern rather than a language (as is the case with JSON), there is no standard.

    It’s name implies that you’ll get a valid JSON object wrapped in a function call.

    Indeed, the “specification” which tells you what will be included in the response should be something for the API you’re subscribing to to document.

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