An async require.js declaration of Bing Maps, requires jQuery deferreds.

microsoft.maps.7.js

define('bingMaps',['async!//ecn.dev.virtualearth.net/mapcontrol/mapcontrol.ashx?v=7.0!OnScriptLoad'], function() {
    var mapReadyDfd = $.Deferred(),
        mapReadyTest = function () {
            if (window.Microsoft && window.Microsoft.Maps && window.Microsoft.Maps.Location) {
                mapReadyDfd.resolve(window.Microsoft.Maps);
            }
            else {
                setTimeout(mapReadyTest, 100);
            }
        };

    mapReadyTest();

    return mapReadyDfd.promise();
});