javascript 数据类型

Posted 2021-02-17 Rosendolu

思维导图 : javascript数据类型

基本数据类型

  var a =1 // "number"

  var b ="" // "string"

  var c =true // "boolean"

  
  var e // "undefined"

  var s = Symbol() // "symbol"

var d = null // "object"
  
// 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.toString.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]"