如何等待异步调用循环完成

Question

我有一个在循环中调用另一个函数的函数。另一个函数进行异步调用。如何等待或知道循环中的每个异步调用何时完成？我尝试在外部函数上进行实验并使用变量赋值，它将返回true，希望它等待该函数的所有内容完成，并在继续执行到下一行sortDrivers之前为变量赋值获取值（），但这似乎并没有像希望的那样发挥作用。

function getData() {
    var url = encodeURI("viewData.aspx");
    $.get(url, function (data) {
        checkForLogin(data);
        $("#ajaxResults").html(data);
        checkForOrphans();

        // setRoute loops making async calls, returns true when done
        var holdUp = setRoute();

        // should not execute until all async calls inside setRoute are done
        sortDrivers();
    });
}

// builds direction request for each driver
function setRoute() {
    var drivers = $("#ajaxResults").find(".driverSection");
    for (var x = 0; x < drivers.length; x++) {
        var driver = $(drivers[x]).attr('id');
        var dlat = $(drivers[x]).find('.dlat');
        var dLatLng = new google.maps.LatLng($(dlat[0]).text(), $(dlat[0]).next().text());
        var stops = [];
        var transactions = $(drivers[x]).find(".transactions");
        for (var y = 0; y < transactions.length; y++) {
            var tlat = $(transactions[y]).find('.tlat');
            var tLatLng = new google.maps.LatLng($(tlat[0]).text(), $(tlat[0]).next().text());
            stops.push({ location: tLatLng, stopover: true });
        }
        request = {
            origin: dLatLng,
            destination: cLatLng,
            waypoints: stops,
            travelMode: google.maps.DirectionsTravelMode.DRIVING
        };

        // this will make an async call to directions service

        getEtas(request, $(drivers[x]).attr('id'));
    }
    return true;
}

function getEtas(request, driver) {
    var totalTime = 0;
    var totalTimeDisplay = "";
    var directionsService = new google.maps.DirectionsService();
    directionsService.route(request, function (response, status) {
        if (status == google.maps.DirectionsStatus.OK) {
            var tEtas = $("#" + driver).find('.tEta');
            for (var x = 0; x < response.routes.length; x++) {
                for (var z = 0; z < response.routes[x].legs.length; z++) {
                    var nextLeg = parseInt(response.routes[x].legs[z].duration.text);
                    if (z < response.routes[x].legs.length - 1 && z > 0) {
                        totalTime = totalTime + nextLeg + 3;
                    }
                    else {
                        totalTime = totalTime + nextLeg;
                    }
                    if (totalTime == 1) {
                        totalTimeDisplay = totalTime + " Min";
                    }
                    else {
                        totalTimeDisplay = totalTime + " Mins";
                    }
                    $(tEtas[z]).text(totalTimeDisplay);
                }
            }
            var dEtas = $("#" + driver).find(".dEta");
            $(dEtas[0]).text(totalTimeDisplay);
        }
    });
}