javascript 数据类型

基本数据类型

var a =1 // "number"

var b ="" // "string"

var c =true // "boolean"

var d = null // "object"

var e // "undefined"

var s = Symbol() // "symbol"

// 注意
null == undefined // true
null == {} // false
undefined == {} //false

引用数据类型

var o = {"a":1} // "object"

数据类型判断

1. typeof

    typeof null  //   "object"
   
    typeof [] //    "object"
   
    typeof {} //   "object"

2. instanceof

   不能检测 null undefined

    // object
   ({}) instanceof Object //    true
   
    //null
    null instanceof Object //    false
   
    //array
    [] instanceof Array //     true
   
    //error
    null instanceof Null
    VM1344:1 Uncaught ReferenceError: Null is not defined
        at <anonymous>:1:17
    (anonymous) @ VM1344:1
    undefined instanceof Undefined
    VM1366:1 Uncaught ReferenceError: Undefined is not defined
        at <anonymous>:1:22

3. Object.protorype.toSting.call() 最靠谱，最常用

   Object.prototype.toString.call("fd") //     "[object String]"
    Object.prototype.toString.call(1) //     "[object Number]"
    Object.prototype.toString.call(true) //     "[object Boolean]"
    Object.prototype.toString.call(null) //     "[object Null]"
    Object.prototype.toString.call(undefined) //     "[object Undefined]"
    Object.prototype.toString.call(Symbol()) //     "[object Symbol]"
    Object.prototype.toString.call({}) //     "[object Object]"

javascript 数据类型

原文：https://www.cnblogs.com/rosendolu/p/10739488.html