How to check if all options are selected on woocommerce variable product [closed]

I am building a custom "Buy Now" plugin on woocommerce, when user clicks "Buy Now" button before going to checkout I want check if user selected variables. If he/she did not, alerts user choose options as add to cart or original buy now button does

You need to use javascript to achieve this

1. override the WooCommerce product template to add a custom buy now button
2. add click event on that buy now button and check if any variation option is selected or not.
3. IF not give alert to the user
4. If yes send an ajax call to add that product to the cart
5. on success redirect the user to the checkout page

let's assume you give the button id as wc_buynow

$(document).on('click','#wc_buynow',function(){
    let is_valid = 1;
    $('select.wc-default-select').each(function(i){
        if($(this).val() == ''){
            let id = $(this).attr('id');
            let attr_name = $("label[for='"+id+"']").text();
            alert(attr_name+" is required!");
            is_valid = 0;
        }
    });

    if(is_valid){
      // send ajax call to add product in cart and on success redirect to checkout
    }

    
})