数据类型

        //typeof 用于查询值的类型

        // undefined类型 未赋值
        var a;
        console.log(typeof (a));
        //number 数字类型
        var b = 11;
        console.log(typeof (b));
        //string 字符串类型
        var d = 'qwe'
        console.log(typeof (d));
        //对象 null，数组都属于object 类型
        var e = [1, 2, 3]
        var c = null
        var date = new Date()
        console.log(typeof (date));
        console.log(typeof (e));
        console.log(typeof (c));