Why doesn't the value of the variable change?

Question

JavaScript

Why doesn't the value of the totalAllProducts variable change?
ajax returns correct data. But totalAllProducts doesn't change

counterTotal() {
        let a = 0;
        let idProduct = 1;
        var totalAllProducts = 0;
        //get cart
        if ($.cookie('cart') != undefined) {
            var cart = JSON.parse($.cookie('cart'));
        } else {
            var cart = 0;
        }
        if (cart != 0) {
            for (var i = 0; i < cart.length; i++) {
                $.ajax({
                url: '/getProduct',
                type: "POST",
                data: {'id': cart[i].id},
                success: function(result) {
                		 totalAllProducts = totalAllProducts + Number(result);
                    }
              });
                // let total = cart[i].price * cart[i].quantity;
                // console.log(cart[i].price);
            }
            console.log(totalAllProducts);
        }
    }

Answer 1

Because asynchrony.
This question comes up here two or three times a week.
At the time console.log was called, the data had not yet arrived from the server. Upon arrival of data, the anonymous callback specified in success will be called, then the variable will receive its value.