<!DOCTYPE html>
<html>
<body>
<h1>JavaScript</h1>
<p>如果将值设置为 <b>undefined</b>，则可以清空变量。</p>
<p id="demo"></p>
<script>
let car = "Volvo";
car = undefined;
document.getElementById("demo").innerHTML = car + "<br>" + typeof car;
</script>
</body>
</html>