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

number類型

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

function類型

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

undefined類型

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

Array類型

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

null類型

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

RegExp類型

var a = /a/g
a instanceof RegExp

Object類型

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

註意：Object,Array,null,RegExp都會判斷為Object，請把Object放在最後一種類型判斷

javascript基礎類型判斷