typeof
typeof ''
"string"
typeof 1
"number"
typeof Symbol
"function"
typeof true
"boolean"
typeof undefined
"undefined"
typeof []
"object"
typeof null
"object"
typeof function(){}
"function"
typeof new Date()
"object"
typeof new RegExp()
"object"
instanceof
A instanceof B A是否是B的实例 通过查找原型链进行判断
[] instanceof Array
true
new Date() instanceof Date
true
[] instanceof Object
true
new Object() instanceof Object
true
let a = {a:1}; a instanceof Object
true
constructor
根据construction判断 根据查找原型的construction属性
但是可能construction会被重写导致该判断失败
null和undefined没有construction属性
new Function().constructor == Function
true
[].constructor == Array
true
Object.prototype.toString
Object.prototype.toString.call("")
"[object String]"
Object.prototype.toString.call([])
"[object Array]"
Object.prototype.toString.call(function a(){})
"[object Function]"
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]"
