tryjsref_undefined 在线代码实例

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运行代码

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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>W3Cschool教程(w3cschool.cn)</title>
</head>
<body>
<script>
var t1="";
var t2;
if (t1===undefined){
    alert("t1 is undefined");
}
if (t2===undefined){
    alert("t2 is undefined");
}
</script>
</body>
</html>
 
 
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运行结果
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