html运行实例（eg_js_datatypes_undefined

代码示例：（标识：eg_js_datatypes_undefined_1）

<!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>