var a = "a"
 typeof  a === "string"

number类型

 let a = 111
 typeof  a === "number"

function类型

 var a = function(){}
 typeof  a === "function"

undefined类型

var a =undefined
 typeof  a === "undefined"
a === undefined

Array类型

var a = []
a instanceof Array
Array.isArray(a)

null类型

var a =null
a instanceof null
a === null

RegExp类型

var a = /a/g
a instanceof RegExp

Object类型

var a = {}
typeof a === "object"
a instanceof Object

注意：Object,Array,null,RegExp都会判断为Object，请把Object放在最后一种类型判断

javascript基础类型判断

原文：http://blog.51cto.com/13661873/2089344