Well, the JS SDK will be more popular. Not everyone develops their server-side code in PHP (can use Java / Scala /. NET / Python / etc, etc.), but everyone needs to write their client-side code in JavaScript.
As for the benefits of both, you can certainly use the JavaScript SDK.
- Less load on your server.
- The best response time, because the request comes directly from the client’s browser on Facebook, and not from the browser => your server => Facebook and vice versa.
Of course, there are times when you have to do something on the server side, either because you want to save the result in your database, or in your security-vulnerable operation. (for example, you will never pass your access_token application to the client and will not use it from there as its secret).
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