ES6-标准入门·Class 类

class Point {
  constructor() {}
  toString() {}
}

typeof Point // function
Point === Point.prototype.constructor // true

// 等同于
Point.prorotype = {
  constructor() {},
  toString() {}
}

class Point {}
let p = new Point()
p.constructor === Point.prototype.constructor // true

Object.assign(Point.prototype, {
  toString()
})

class Foo {
  constructor() {
    return Object.create(null)
  }
}
new Foo() instanceof Foo // false

class Point {
  constructor(x) {
    this.x = x
  }
  toString() {}
}
const p = new Point(1)
p.hasOwnProperty('x') // true
p.hasOwnProperty('toString') // false
p.__proto__.hasOwnProperty('toString') // true

const MyClass = class Me {
  getClassName() {
    return Me.name
  }
}

const inst = new MyClass()
inst.getClassName() // Me
Me.name // ReferenceError: Me is not defined

// 省略 Me
const MyClass = class {}

// 立即执行 Class
const p = new (class {})()

// 确保父类在子类之前定义
const Foo = class {}
class Bar extends Foo {}

const bar = Symbol('bar')

class Point {
  foo() {
    this[bar]()
  }

  [bar]() {}
}

class Logger {
  printName() {
    this.print()
  }
  print() {
    console.log('Hello')
  }
}
const logger = new Logger()
const { printName } = logger
printName() // TypeError: Cannot read property 'print' of undefined

class Logger {
  constructor {
    this.printName = this.printName.bind(this)
  }
}

function selfish(target) {
  const cache = new WeakMap()
  const handler = {
    get(target, key) {
      const value = Reflect.get(target, key)
      if (typeof value !== 'function') return value
      if (!cache.has(value)) cache.set(value, value.bind(target))
      return cache.get(value)
    }
  }
  return new Proxy(target, handler)
}
const logger = selfish(new Logger())

function Person(name) {
  if (new.target === Person) {
    this.name = name
  } else {
    throw new Error('必须使用 new 生成实例')
  }
}

class Shape {
  constructor() {
    if (new.target === Shape) {
      throw new Error('本类不能实例化')
    }
  }
}

class Rectangle extends Shape {
  constructor(length, width) {
    super()
  }
}

class Point {}
class ColorPoint extends Point {
  constructor() {}
}
const cp = new ColorPoint() // ReferenceError

class ColorPoint extends Point {}

// 等同于
class ColorPoint extends Point {
  constructor(...args) {
    super(...args)
  }
}

Object.getPrototypeOf(ColorPoint) === Ponit // true

class A {
  constructor() {
    console.log(new.target.name)
  }
}

class B extends A {
  constructor() {
    super()
  }
}

new A() // A
new B() // B

class Parent {
  static myMethod(msg) {
    console.log('static', msg)
  }
  myMethod(msg) {
    console.log('instance', msg)
  }
}

class Child extends Parent {
  static myMethod(msg) {
    super.myMethod(msg)
  }
  myMethod(msg) {
    super.myMethod(msg)
  }
}

Child.myMethod(1) // static 1
const child = new Child()
child.myMethod(2) // instance 2

class A {
  constructor() {
    // 无法获得
    this.p = 2
  }
}
// 可以获得
A.prototype.p = 2

class A {
  constructor() {
    this.x = 1
  }
}
class B extends A {
  constructor() {
    super()
    this.x = 2
    super.x = 3
    console.log(super.x) // undefined
    console.log(this.x) // 3
  }
}

class A {}
class B extends A {}
B.__proto__ === A // true
B.prototype.__proto__ === A.prototype // true

// B 的实例继承 A 的实例
Object.setPrototypeOf(B.prototype, A.prototype)
// B 的实例继承 A 的静态属性
Object.setPrototypeOf(B, A)

Object.setPrototypeOf = function(obj, proto) {
  obj.__proto__ = proto
  return obj
}

Object.setPrototypeOf(B.prototype, A.prototype)
// 等同于
B.prototype.__proto__ = A.prototype

Object.setPrototypeOf(B, A)
// 等同于
B.__proto__ = A

class A extends Object {}
A.__proto__ === Object // true
A.prototype.__proto__ === Object.prototype // true

class A {}
A.__proto__ === Function.prototype // true
A.prototype.__proto__ === Object.prototype // true

class A extends null {}
A.__proto__ === Function.prototype // true
A.prototype.__proto__ === undefined // true

const p1 = new Point(2, 3)
const p2 = new ColorPoint(2, 3, 'red')
p2.__proto__ === p1.__proto__ // false
p2.__proto__.__proto__ === p1.__proto__ // true

function mix(...mixins) {
  class Mix {}
  for (let mixin of mixins) {
    copyProperties(Mix, mixin)
    copyProperties(Mix.prototype, mixin.prototype)
  }
  return Mix
}
function copyProperties(target, source) {
  for (let key of Reflect.ownKeys(source)) {
    if (key !== 'constructor' && key !== 'prototype' && key !== 'name') {
      let desc = Object.getOwnPropertyDescriptor(source, key)
      Object.defineProperty(target, key, desc)
    }
  }
}

class DistributedEdit extends mix(Loggable, Serializable) {
  // ...
}