JS的toString方法

基本数据类型

Number

• Number.prototype.toString === new Number(123).__proto__.toString

const num = 123
console.log(num.toString()) // '123' 

String

• String.prototype.toString === new String('hello').__proto__.toString

const str = 'hello'
console.log(str.toString()) // 'hello'

Boolean

• Boolean.prototype.toString === new Boolean('hello').__proto__.toString

const boo= true
const boo1 = false
console.log(boo.toString()) // 'true'
console.log(boo1.toString()) // 'false'

null和undefined

• null和undefined这两种数据类型没有包装类，所以无法调用包装类上的方法

null.toString()  // Cannot read property 'toString' of null

undefined.toString() // Cannot read property 'toString' of undefined

引用数据类型

Object

• Object.prototype.toString === new Object({a: 1}).__proto__.toString
• Object.toString() => "function Object() { [native code] }"

let obj = {
	a: 1
}
obj.toString() // '[object Object]'

Array

• Array.prototype.toString === new Array([1, 2]).__proto__.toString

let arr = [1,2]
arr.toString() // '1,2'

Function

• Function.prototype.toString === new Function(function(){}).__proto__.toString

let func = function(){}
func.toString() // 'function(){}'