1. Typeof view variable type?

1.typeof There are seven types of return values for ：

number, boolean, string, undefined, object, function,symbol.

1、number

typeof(10);
typeof(NaN);
//NaN stay JavaScript Represents a special non numeric value , It is itself a numeric type .
typeof(Infinity);

2、boolean

typeof(true);
typeof(false);

3、string

typeof("abc");

4、undefined

typeof(undefined);
typeof(a);// Variables that don't exist 

5、object

 object , Array ,null return object
typeof(null);
typeof([]);
typeof({
    });
typeof(window);

6、function

typeof(Array);
typeof(Date);

7、symbol

typeof Symbol() // ES6 New types of offers