title: How to execute a code on focus of textarea just once?
body: <p>I have a teatarea like this:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>$("textarea").on('focus', function(){
    alert("clicked");
  });</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"&gt;&lt;/script&gt;
  &lt;textarea col="3" row="20"&gt;&lt;/textarea&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>As you see in the above fiddle, every time when you focus on that textarea, <code>alert()</code> executes. How can I limit it to executes just one time? <em>(just first time)</em></p>