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JS中null NaN undefined这三个值有什么区别
2022-07-07 14:15:00 【Vayne的胖虎子】
我们在JS数据类型中肯定会遇到比较陌生的面孔,比如NaN和undefined,对于null我们在Java中就早早接触过,那么我们来通过代码看一下这三个东西有什么关系和区别呢?
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>null NaN undefined这三个值有什么区别</title>
</head>
<body>
<script type="text/javascript">
// == 是等同运算符
alert(1 == true); // true
alert(1 === true); // false
// null NaN undefined 数据类型不一致.
alert(typeof null); // "object"
alert(typeof NaN); // "number"
alert(typeof undefined); // "undefined"
// null和undefined可以等同.
alert(null == NaN); // false
alert(null == undefined); // true
alert(undefined == NaN); // false
// 在JS当中有两个比较特殊的运算符
// ==(等同运算符:只判断值是否相等)
// ===(全等运算符:既判断值是否相等,又判断数据类型是否相等)
alert(null === NaN); // false
alert(null === undefined); // false
alert(undefined === NaN); // false
</script>
</body>
</html>
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