How to show/hide text based on variant selection Impulse theme

Store Design
1

I am trying to show a "Pre-Order " message on top of Add-To-Cart button based on the inventory level of a variant

Here is a link to the store - https://ct81qz9fsunxvmsw-10155047.shopifypreview.com/products/the-single-edge-pro-1

I added the code below to the theme.js file but it does not seem to work - I tried adding a custom Javascript file with the code and still not working (getting an Uncaught ReferenceError)

_updateMessage: function(variant) {
   var stockMessage = document.getElementById('stockMessage');

   if (variant.inventory_quantity > 0 ) {
      $stockMessage.hide();
   } else if (variant.inventory_quantity <= 0) {
      $stockMessage.show();
};
},

Please anyone assist with this