All Shopify cart ajax | https://shopify.dev/docs/themes/ajax-api/reference/cart

Multiple_line_properties.js

// Using add.js queue
// Use this with assumption that you will not edit  or add product after it has ben added to the cart.
$('body').on('click', '.update_desk', function(event) {
    event.preventDefault();
    var thiss = $(this);
    Shopify.queue = [];
    //var quantityInCart = parseInt($('#cnt-crt-itm').data("cart-count"));
    var productHandle = "."+$(this).attr("data-product-handle");
    var loader = $(".loader-"+$(this).attr("data-product-handle"));
    loader.css('display', 'block');

    jQuery(productHandle).find('.qty_desk').each(function(index){
        var id = parseInt($(this).attr('data-variant-id'));
        var quantity = parseInt($(this).val());
        var lineProp = $(this).attr('data-line-prop');
        Shopify.queue.push({
            variantId: id,
            variantQty: quantity,
            variantLine: lineProp,
        });
    });
    Shopify.moveAlong = function() {
        // If we still have requests in the queue, let's process the next one.
        if (Shopify.queue.length) {
            var request = Shopify.queue.shift();
            var data = 'id='+ request.variantId+'&quantity='+request.variantQty+'&properties[Order Status]='+request.variantLine;
            $.ajax({
                type: 'POST',
                url: '/cart/add.js',
                dataType: 'json',
                data: data,
                success: function(res){
                    Shopify.moveAlong();
                    //quantityInCart += 1;
                },
                error: function(){
                    // if it's not last one Move Along else update the cart number with the current quantity
                    if (Shopify.queue.length){
                        Shopify.moveAlong()
                    } else {
                       //jQuery('.count').html(quantityInCart);
                    }
                }
            });
        } else {
            addToCartOk();
        }
    };
    Shopify.moveAlong();
    function addToCartOk(){  
        jQuery.getJSON('/cart.js', function(cart) {
            jQuery('.count').html(cart.item_count);
            var number = cart.total_price/100;
            jQuery('.totalmoney').html("$"+number.toLocaleString()+", ");
            loader.css('display', 'none');
            thiss.val("UPDATE");
        });
    } 
});

Multiple_product.js

// We use update.js to update/add multiple product
// Note that update.js can't add/update line properties, but note and attributes can.

$('body').on('click', '.update_desk', function(event) {
    event.preventDefault();
    // Some identifications
    var thiss = $(this);
    var productHandle = "."+$(this).attr("data-product-handle");
    var loader = $(".loader-"+$(this).attr("data-product-handle"));
    var length = jQuery(this).parents('.all-sizes').find('.qty_desk').length;
    var data = "";
    // Get list of products, put as string.
    jQuery(productHandle).find('.qty_desk').each(function(index){
        var id = parseInt($(this).attr('data-variant-id'));
        var quantity = parseInt($(this).val());
        data += "updates["+id+"]="+quantity+"&";
    });
    // Remove last characte becuase it is '&'
    var dataFinal = data.slice(0, data.length-1);
    $.ajax({
        url: "/cart/update.js",
        type: "POST",
        data: dataFinal,
        dataType: 'json',
        beforeSend: function() {
            loader.css('display', 'block');
        },
        error: function(T) {
            console.log(T);
        },
        success: function(data){
            console.log(data)
        }
    });
});