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Your question is unrealted to Codeigniter. You will need client side Javascript for this. In Jquery you could do it like this:

Code:

$(".button").click(function(e) {

   e.preventDefault();

   $('#result').html('<img src="/ajax-loader.gif" alt="Loading"/>');
   
   $.ajax({
       type: "POST",
       url:  '/yourUrl' ,
       data: { YourDataArray},
       success: function (data) {
           $('#result').html(data);
       },
       error: function (xhr, status) {
           $('#result').html('Error, somethign went wrong');
       }
   });