JQuery代码小问题

Question

$(document).ready(function () {            var ID = $("#txtID").val();            var url = $.format("../../Controls/InfoHandler.ashx?param={0}", "getinfo");            $.getJSON(url, function (data, status) {                for (var i = 0; i < data.length; i++) {                    $("#dsize").append(                        "<div id="+data[i].InvID+">" + data[i].Size + "</div>"                        );                }            });            var $sizedivs = $("#dsize>div");//.children("div");            var abc = $sizedivs[0];            alert(abc.id);        });这段代码直接执行为什么不弹出窗口呢   在var $sizedivs = $("#dsize>div");//.children("div");处设个断点再执行就可以弹出窗口