重學第六章

1. 原型

• 實例內屬性和原型上屬性重名時（屏蔽）

function Test(name) {this.name = name
}
Test.prototype.name = 'hhh'
let tObj = new Test('yyy')
console.log(tObj.name) // yyy
tObj.name = null
console.log(tObj.name) // null
delete tObj.name
console.log(tObj.name) // hhh

• 實例的__proto__屬性指向的對象有constructor屬性，指向構造函數

function Test() {}
let tObj = new Test()
console.log('實例', tObj)
console.log('constructor', tObj.constructor)
console.log(tObj.constructor === tObj.__proto__.constructor)

• 實例（實例化的時候）的__proto__ 和構造函數的prototype全等，

function Test() {}
Test.prototype.name = 'name'
let tObj = new Test()
console.log('實例', tObj)
console.log('實例__proto__', tObj.__proto__)
console.log('prototype', Test.prototype)
console.log(tObj.__proto__ == Test.prototype)

• 切斷了prototype 和 __proto__的聯系，并且丟失了constructor

• 手動在字面量里添加constructor會讓這個屬性的[[Enumerabl]]變為true

• 可用Object.defineProperty(Car.prototype,constructor,{
  enumerable:false,value:Car})
  
  
  
  
  
  不加debugger
  

• 在實例化之后再改prototype （跟實例化前后也有點關系）
  

function Test() { }
Test.prototype.name = 'hhh'
Test.prototype = {name: '111'
}
let tObj = new Test()
Test.prototype.name = '666'
console.log(tObj.name) // 666
console.log(tObj.__proto__ === Test.prototype) // true
console.log(Test.prototype.isPrototypeOf(tObj)) // true  

function Test() { }
Test.prototype.name = 'hhh'
Test.prototype = {name: '111'
}
let tObj = new Test()
Test.prototype = {name: '666'
}
console.log(tObj.name) // 111
console.log(tObj.__proto__ === Test.prototype) // false
console.log(Test.prototype.isPrototypeOf(tObj)) // false  

2. 插件開發

• 放在IIFE里，能隔離作用域
  

; (function () {function Compute(a, b) {this.a = athis.b = b}Compute.prototype.plus = function () {return this.a + this.b}Compute.prototype.minus = function () {return this.a - this.b}Compute.prototype.multi = function () {return this.a * this.b}Compute.prototype.div = function () {return this.a / this.b}window.Compute = Compute
})()
let computeObj = new Compute(8, 2)
console.log('加', computeObj.plus()) // 10
console.log('減', computeObj.minus()) // 6
console.log('乘', computeObj.multi()) // 16
console.log('除', computeObj.div()) // 4