javascript 数据类型 随笔

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

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     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]"
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