Character Count with Live Progress Bar using jQuery

Javascript

jQuery(document).ready(function() {
    
    $('textarea').keyup(function() {
        var box = $(this).val();
        var main = box.length * 100;
        var value = (main / 100);
        var count = 0 + box.length;
        var reverse_count = 100 - box.length;
        
        if(box.length >= 0){
            $('.progress-bar').css('width', count + '%');
            $('.current-value').text(count + '%');
            $('.count').text(reverse_count);
            
            if (count >= 50 && count < 85){
                $('.progress-bar').removeClass('progress-bar-danger').addClass('progress-bar-warning');
            }
            if (count > 85){
                $('.progress-bar').removeClass('progress-bar-warning').addClass('progress-bar-danger');
            }
            if(count >= 0 && count < 50){
                $('.progress-bar').removeClass('progress-bar-danger');
                $('.progress-bar').removeClass('progress-bar-warning');         
                $('.progress-bar').addClass('progress-bar-success')
            }
            
        }
        return false;
    });
});

HTML

<div class = "col-md-6">        
    <div class="progress">
        <div class="progress-bar progress-bar-striped active" role="progressbar" aria-valuenow="0" aria-valuemin="0" aria-valuemax="100" style="width: 0%;">
            <span class = "current-value">0%</span>
        </div>
    </div>
    <div class = "form-group">
        <textarea class = "form-control" rows = "7" maxlength = "100" placeholder = "Enter a text"></textarea>
    </div>
    <div class = "count btn btn-primary">100</div>
</div>