title: How to develop alert system like facebook using PHP and Jquery?
body: <p>How can I develop an alert system like Facebook's, where User A add User B, User B will get some number in Friend Request Section on the header like in the image below. How can I develop something like that? 
  How can we get numbers like this??how can i get codes in PHP and JQuery?
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  <img src="https://i.stack.imgur.com/hu2eb.gif" alt="alt text"></p>