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Editorial Team
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Asked: 2026-05-22T00:45:27+00:00

We are developing a web app ( http://beta.dammela.it ) which use both FB Graph

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We are developing a web app (http://beta.dammela.it) which use both FB Graph api server side, FB Javascript SDK and social plugins.

The integration with FB is deep and we would like to detect when a user visiting our website is behind a proxy which block all traffic to Facebook properties (like in some working place).

If we could detect he is blocked we could give him/her some hints, help, explanation and some alternative methods to login and interact with the application.

But I can’t figure out how to do that.

I guess, but is just my guess, there’s a way to detect if the user access to Facebook is blocked checking something in the Javascript SDK, but I have not been able to find out what and/or how.

Any idea?

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1 Answer

  1. Editorial Team

    Explaination:
    We try to download the facebook favicon. If it throws an error then we know that facebook is blocked.
    Note: When a proxy blocks a URL then it return an error in 4xx range back to the client.

    Code: 

    var img = new Image();
img.onerror = function () {
 alert("It seems Facebook is blocked!"); 
}
img.src = "http://facebook.com/favicon.ico";

    You can try this out here.

    Update: Replaced server-side C# code with client-side JavaScript.

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