AJAX 순서 확인

function getCustomers() {
    var request = new XMLHttpRequest();

// 1)

    request.open("GET", "customer/list"); 

    request.onreadystatechange = function () {
        if (request.readyState === 4) {
            try {

// 3)

                var response = JSON.parse(request.responseText);
                if (request.status === 200) {
                    customers = response.customers;
                    displayCustomers();
                } else {
                    alert(response.message);
                }
            } catch (exception) {
                alert("Customer list not available.");
            }
        }
    };

//   2)

request.send();

    //if (request.status != 200) {
    //    alert("Error " + request.status + " - " + request.statusText);
    //}
}