<div class="container">
  <div class="row">
    <div class="col-xs-12">
      <h1 class="page-header">jQuery Chained Select</h1>
    </div>
  </div>
  <div class="row">
    <div class="col-xs-3">
      <form action="" id="addToCart">
        <div class="form-group">
          <select name="color" id="size" class="form-control">
            <option value="">Size</option>
            <option value="Small">Small</option>
            <option value="Medium">Medium</option>
            <option value="Large">Large</option>
            <option value="X-Large">X-Large</option>
          </select>
        </div>
        <div class="form-group">
          <select name="color" id="color" class="form-control" disabled>
            <option value="">Color</option>
            <option value="Red">Red</option>
            <option value="Blue">Blue</option>
            <option value="Green">Green</option>
          </select>
        </div>
        <div class="form-group">
          <select name="qty" id="qty" class="form-control" disabled>
            <option value="">Quantity</option>
            <option value="1">1</option>
            <option value="2">2</option>
            <option value="3">3</option>
            <option value="4">4</option>
          </select>
        </div>
        <div class="form-group">
          <button type="submit" id="submit" class="btn btn-default" disabled><i class="glyphicon glyphicon-shopping-cart"></i> Add to Cart</button>
        </div>
      </form>
    </div>
  </div>
</div>

function chainSelect(current, target){
  var value1 = $(current).on('change', function(){
    if($(this).find(':selected').val() != ''){
      $(target).removeAttr('disabled');
      var value = $(this).find(':selected').text();
    }else{
      $(target).prop('disabled', 'disabled').val(null);
    }
  return value;
  });
  return value1;
}
size = chainSelect('select#size', '#color');
color = chainSelect('select#color', '#qty');
qty = chainSelect('select#qty', '#submit');

$('#addToCart').submit(function(){
  event.preventDefault();
  alert('Size: ' + size + 'nColor: ' + color + 'nQuantity: ' + qty);
});