如果我从以下脚本中取出警报,那么firebug说结果是未定义的？`
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>Inventory Management</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<title>Untitled Document</title>
<script src="json.js" type="text/javascript"></script>
<script src="prototype.js" type="text/javascript"></script>
</head>
<body>
<div id="content">
<div id="header">
</div>
<script type="text/javascript">
var xhr;
var results=getPlants(xhr,results);
var plants=[];
function getPlants(xhr,results){
try {
xhr=new XMLHttpRequest();
}catch(microsoft){
try{
xhr=new ActiveXObject("Msxml2.XMLHTTP");
}catch(othermicrosoft){
try{
xhr = new ActiveXObject("Microsoft.XMLHTTP");
}catch(failed){
xhr=false;
alert("ajax not supported");
}
}
}
xhr.onreadystatechange= function () {
if(xhr.readyState==4 && xhr.status==200) {
results = xhr.responseText;
}
}
xhr.open("GET","db_interactions.php",true);
xhr.send(null);
alert("sent");
return …