i'm trying to update img cover without refresh the page using ajax and php but it does not work at all
HTML
  <div class="cover" >
  <img  id="b1"  src="<?php echo $user->picture_path();>"class="cover"/>          
                <div id="modal-cover" class="cov-lo">        </div>
   </div>
js
$('#b2').on({
    'click': function(){ 
     $('#b1').attr('src', <?php echo $user->picture_path();?> + '?' + new Date().getTime());}
});
the input and form
   <form  action="profile.php" method="POST" enctype="multipart/form-data"  > 
            <div class="hio"> 
                                        Upload                                   <input  type="file" onchange="this.form.submit()" name="cover" id="bla2"class="custom-file-input" /> 
 </div> 
             </form>
 
     
     
    