Hello! So, here I am again! Sorry for the delay, almost 2 months since I last posted here. Anyway, I here today to talk about CORS and JSONP. Basically I will introduce the terms and cite some implementation examples using JavaScript and ASP.NET WebAPI (because I am a .NET fan, of course!).


First I will talk about JSONP. The acronym stands for “JSON with padding”. We have a lot of resources telling about the concept in the internet today, so I will be short. “JSON with padding” its basically a hack that makes possible inter-domain requests. And that’s it. This hack consists from return a function (often named ‘callback’ or whathever you want) that receives a JSON parameter like the following.

A lot of APIs from well know companies like Instagram and Github provides JSONP APIs to developers. Click here to access a list of JSON APIs available today. The main advantage to use JSONP is the the compatibility with some old browsers like IE 7< and the main disadvantage concerns the security: like I said before JSONP is a hack created when nobody had a option to make cross-domain requests, so the creators didn’t seem to be bothered too much by security.

In the code below you can see a simple example using the polymer-jsonp web component to do a simple JSONP request to the Battelfield 4 API.


Instead of using a hack you can use a better a safe way: CORS. CORS stands for “Cross-Origin Resource Sharing”. CORS introduced a new HTTP header to allow cross-domain requests called “Access-Control-Allow-Origin”.

Using ASP.NET WebAPI, If you want to enable CORS you just need to follow this 3 simple steps:

  1. Install the package Microsoft.AspNet.WebApi.Cors using NuGet;

  2. Insert the following line of code in our WebApiConfig located in the App_Start folder:

  1. Insert the EnableCorsAttribute in all ours Controllers that you interested in enabling CORS.

So, thats it! If you have any questions you are free to ask in the commentary box below.

Have a nice day!

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