gistfile1.js

  jQuery(function() {
    // This first bit is just handling the user selecting a variant.
    $('.product-information').on('click', '.variant_title', function(e) {
      e.preventDefault();
  	$(this).addClass('selected').siblings().removeClass("selected");
      	$(this).closest('.product-information').find('#bis_button').toggle($(this).is('.unavailable'));
    });
    
    // Then, when the button is clicked... 
    $('#bis_button').on('click', function(e) {
     e.preventDefault(); 
      
     var email = prompt('Please enter your email address');
     
     // ...find out which variant is currently selected, and fetch that product and variant ids off the element.
     var selectedVariant = $(this).closest('.product-information').find('a.variant_title.selected');
     var productId = selectedVariant.data("product-id"),
         variantId = selectedVariant.data("variant-id");
      
     console.log(email, productId, variantId);
      
     // Finally, call BISPopover.create() and handle the response.
     
     BISPopover.create(email, variantId, productId).then(function(data) {
        if (data.status == "OK") {
          alert(data.message); 
        } else {
		  var msg = [];
           for(var i in data.errors) {  // could be more than one error message
                msg.push(data.errors[i]);
           }          
           alert(msg);
        }

      });

    })
  });