// using a pure CSS selector  
   if ($('p:visible')) {  
      alert('Paragraphs are visible (checked using a CSS selector) !');  
   };  
  
   // using jQuery's is() method  
   if ($('p').is(':visible')) {  
      alert('Paragraphs are visible (checked using is() method)!');  
   };  
  
   // using jQuery's filter() method  
   if ($('p').filter(':visible')) {  
      alert('Paragraphs are visible (checked using filter() method)!');  
   };  
  
   // you can use :hidden instead of :visible to reverse the logic and check if an element is hidden  
   // if ($('p:hidden')) {  
   //    do something  
   // };  

$(document).ready(function()
{
    $("#toggle").click(function()
    {
        $("#content").toggle();
    });

    $("#visiblity").click(function()
    {
       if( $('#content').is(':visible') )
       {
          alert("visible"); // Put your code for visibility
       }
       else
       {
          alert("hidden");
       }
    });
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.2/jquery.min.js"></script>

<p id="content">This is a Content</p>

<button id="toggle">Toggle Content Visibility</button>
<button id="visibility">Check Visibility</button>

$(document).ready(function() {
   var visible = $('#tElement').is(':visible');

   if(visible) {
      alert("visible");
                    // Code
   }
   else
   {
      alert("hidden");
   }
});

<script src="https://code.jquery.com/jquery-1.10.2.js"></script>

<input type="text" id="tElement" style="display:block;">Firstname</input>