JSFiddle - React, Tailwind, and code Playground

HTML

<select id="choose-size" class="form-control input-sm">
 <option selected disabled>Select Sizes</option>
 <option>Small</option>
 <option>Medium</option>
 <option>Large</option>
 <option>X Large</option>
</select>

<button id="cart-btn" type="button" class="btn btn-success btn-lg cart-btn" disabled>
ADD TO CART
</button>

JavaScript

$(document).ready(function(){
    console.log($('#cart-btn').prop('disabled'));
    if($('#cart-btn').prop('disabled')){
       
    }
$('input').one('change', function() {
     $('#cart-btn').prop('disabled', false);
     
});
    
});