使用 JavaScript 检查空 XML 数据

Question

>我从XML获取数据。我需要检查数据，如果数据为空，我必须隐藏它。

如何检查？

  <script>
   downloadUrl("gxml.php", function(data) {
       var xml = data.responseXML;
       var markers = xml.documentElement.getElementsByTagName("marker");
       for (var i = 0; i < markers.length; i++) {
         var oid = markers[i].getAttribute("objectid");
         var status = markers[i].getAttribute("status");
         var title = markers[i].getAttribute("title");
         var volume = markers[i].getAttribute("volume");
         var kwh = markers[i].getAttribute("kwh");
         var puser = markers[i].getAttribute("puser");
         var ucomp = markers[i].getAttribute("ucomplate");
         var udate = markers[i].getAttribute("udate");
         var suser = markers[i].getAttribute("suser");
         var scomp = markers[i].getAttribute("scomplate");
         var sdate = markers[i].getAttribute("sdate");
            var type = markers[i].getAttribute("type");
         var point = new google.maps.LatLng(
             parseFloat(markers[i].getAttribute("lat")),
             parseFloat(markers[i].getAttribute("lng")));
         var html = "ObjectID:"  + oid + "  <br/> Title:"  + title +"  <br/>Status:" + status + "  <br/>Volume:" + volume + "  <br/> KWh:" + kwh + "  <br/>User:" + puser + "  <br/> User Date:" + udate + "  <br/> User Complate :" + ucomp + "  <br/>Super user:" + suser + "  <br/> S .User Date:" + sdate + "  <br/> S. User Complate :" + scomp + "<br/> <a href="edit.php">Add/Edit</a>";
</script>
// this data i get from xml. i`m need to chek this null or not null

Answer 1

您可以简单地对任何给定变量进行if (!myVariable)检查。如果返回 true（也就是说，如果代码进入if体，则数据为 null。我要做的是而不是这样做：

var oid = markers[i].getAttribute("objectid");
// ...
..."ObjectID:"  + oid + "

在变量中包含您的标题，如下所示：

var oid = markers[i].getAttribute("objectid");
if (oid) {
    oid = "ObjectID: " + oid;
}

这样，您就可以将oid直接添加到字符串中。如果值为 null，则添加它将不起作用，因为变量将为空。如果有值，则将附加标题，并且执行+ oid将同时附加标题和值。

Answer 2

if ( !foo ) {
    // foo is not set, it is null.
}