Wordpress woocommerce catch change of variation select

gistfile1.txt

$( ".variations_form" ).on( "woocommerce_variation_select_change", function () {
    // Fires whenever variation selects are changed
} );

$( ".single_variation_wrap" ).on( "show_variation", function ( event, variation ) {
    // Fired when the user selects all the required dropdowns / attributes
    // and a final variation is selected / shown
} );

// another trick
$('form.cart').on( 'change', '.variations select', function( event ) {

});