Does JSONP require server modifications?

Question

I understand that jsonp is a technique to get around the same origin policy. You basically refer to your json serving server endpoint in a script tag, because script tags are exempt from the SO policy.

My question is: Assuming a server has an endpoint that serves up json, are there any modifications necessary on the server to make use of jsonp in the client?

I think no, but want to be sure....

Answer 1

Yes, JSONP is slightly different when it renders, so your server needs to support it.

JSON looks like this:

{ "name": "value" }

Whereas JSONP looks like this:

functionName({ "name": "value" });

If whatever you're using supports it you're covered, but it's not the same as supporting just JSON. When the server gets a request, for example: http://example.com/json?callback=functionName, the above is what you should render, because how it looks in the page is this:

<script type="text/javascript" src="http://example.com/json?callback=functionName"&gt;&lt;/script&gt;

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This means something that runs needs to be returned, as an illustration, this is valid:

<script type="text/javascript">
  functionName({ "name": "value" });
</script>

If your server didn't support JSONP it would effectively be this:

<script type="text/javascript">
  { "name": "value" }
</script>

...and you'll get syntax errors, since that's not valid JavaScript.