​x
 
<!DOCTYPE html>
<html>
<body>
​
<h1>JavaScript</h1>
​
<p>undefined 和 null 值相等但类型不同：</p>
​
<p id="demo"></p>
​
<script>
document.getElementById("demo").innerHTML =
typeof undefined + "<br>" +
typeof null + "<br><br>" +
(null === undefined) + "<br>" +
(null == undefined);
</script>
​
</body>
</html>
​