js变量的类型-01 筋斗云网络

js变量的类型-01

null 没有对象的意思

undefind 原声数据没有

dom所声明的全部为null 例如

标签

对象声明用：

调用 .

数组调用[]

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>新建网页</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta name="description" content="布尔教育 http://www.itbool.com" />
</head>
    <body>
     <script>
        var a = 23;
        var b = 3.14;
        var c = 'hello';
        var d = 'world';
        var e = true;
        var f = null;
        var g = undefined;
        var h = {name:'lisi' , age: 29};//对象类型
        console.log(h.name);     //lisi
        console.log(h['name']);   //lisi
        var arr = ['a' , 3 , 'hello' , true];  //始终从0,1.....n 递增不会空缺
        console.log(arr);   //["a", 3, "hello", true]
        console.log(arr[3]);  //  true   0 1 2 3 
     </script>
    </body>
</html>