Dinamic List with Js

dinamic-list.js

var main = function(){
  var btn   = $('.btn');
      
  btn.on('click', function(){
    var post  = $('.status-box');
    
    post.val();
    $('<li>').text(post).prependTo('.posts');
    $('.status-box').val('');
    $('.counter').text('140');
    $('.btn').addClass('disabled'); 
  });
  
  $('.status-box').keyup(function(){
    var postLength      = $(this).val().length,
        charactersLeft  = 140 - postLength;
    
    $('.counter').text(charactersLeft);
    
    if( charactersLeft < 0 ) {
      $('.btn').addClass('disabled');    
    }
     
    else if( charactersLeft == 140) {
      $('.btn').addClass('disabled');        
    }
    
    else {
      $('.btn').removeClass('disabled');    
    }
  });
  
  $('.btn').addClass('disabled');    
};

$(document).ready(main);