JavaScript的7种数据类型

1. string

var a = 'Hello'
console.log(a.length)

2. number

var num = 1 + 3

3. null

typeof null  // object

4. object

var person = {}
person['name'] = 'jack'
person['age'] = 27

5.symbol

6. boolean
   true or false?
   7.undefined

var a //undefined