JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" class="empty" />

CSS

.empty {
   border: 1px solid red;
}

.full {
   border: 1px solid green;
}

input {
   margin: 10px; 
    width; 100px; 
}

JavaScript

var track = function() {
        
        if($(this).val().length == 1){
            $(this).removeClass('empty').addClass('full');
        } else {
            $(this).removeClass('full').addClass('empty');            
        }
    }

$('input').keyup(track);