typeof和instanceof的用法

typeof是一个一元运算，返回值有六种可能： "number," "string," "boolean," "object," "function," 和 "undefined."

instanceof 判断一个变量是否为某个对象的实例。

> typeof null
'object'

> null instanceof Object

'false'

> typeof true
'boolean'

> typeof 123
'number'

> typeof "abc"
'string'

> typeof function() {}
'function'

> typeof {}
'object'

> typeof []
'object'

> typeof Date

'function'

> typeof new Date()

'object'