<!DOCTYPE html>
<html>
<body>
<h2>JavaScript 数据类型</h2>
<p>无值变量的值和数据类型是 <b>undefined</b>。</p>
<p id="demo"></p>
<script>
var car;
document.getElementById("demo").innerHTML =
car + "<br>" + typeof car;
</script>
</body>
</html>