<!DOCTYPE html>
<html>
<body>
<h1>JavaScript</h1>
<p>没有值的变量的值（和数据类型）是 <b>undefined</b>。</p>
<p id="demo"></p>
<script>
let car;
document.getElementById("demo").innerHTML =
car + "<br>" + typeof car;
</script>
</body>
</html>