To create posts using JS

posts.js

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

$(document).ready(main);

posts2.js

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

$(document).ready(main);

This is to create a post with 140 characters and post new succeeding to posts next to each other. Counter resets to 140 after creating a new post.

In the second version, the button is enabled only if the user types something in the post box. The post button is disabled when the characters is more than 140 characters.