Javascript四种设计模式

function Person() {
  this.name = "John";
}

function Singleton(construct) {
  let obj = new construct();
  Singleton = function () {
    return obj;
  }

  return obj;
}

let p1 = new Singleton(Person); // 这里用不用 new 的可以
let p2 = new Singleton(Person);

console.log(p1 === p2);

class Observer {
  constructor(name, fn = () => {}) {
    this.name = name;
    this.fn = fn;
  }
};

class Subject {
  constructor(state) {
    this.state = state;
    this.observers = [];
  }

  setState(newState) {
    if(this.state === newState) return;
    this.state = newState;

    this.observers.map(item => item.fn(newState));
  }

  listen(observer) {
    if (this.observers.indexOf(observer) === -1) {
      this.observers.push(observer);
    }
  }

  unlisten(observer) {
    const index = this.observers.indexOf(observer);
    if (index !== -1) {
      this.observers.splice(index, 1);
    }
  }
};

const p1 = new Observer('小夫', (state) => {console.log(`${state} ==> 小夫--> 打篮球`)});
const p2 = new Observer('胖虎', (state) => {console.log(`${state} ==> 胖虎--> 睡大觉`)});

const s1 = new Subject('学习');

s1.listen(p1);
s1.listen(p2);
console.log(s1);

s1.setState('玩');

s1.unlisten(p1);

s1.setState('学习');

class Subscribe {
  constructor() {
    this.events = {};
  }

  includeEvent(event) {
    return this.events[event] !== undefined;
  }

  notIncludesEvent(event) {
    return this.events[event] === undefined;
  }

  on(event, func) {
    if (this.notIncludesEvent(event)) {
      this.events[event] = [func];
    } else {
      this.events[event].push(func);
    }
  }

  off(event, func) {
    if (this.includeEvent(event)) {
      const index = this.events[event].indexOf(func);
      if (index !== -1) {
        this.events[event].splice(index, 1);
      }
    }
  }

  trigger(event) {
    if (this.includeEvent(event)) {
      this.events[event].map(item => item());
    }
  }
}

let sub = new Subscribe();

function func1() {console.log('func1');}
function func2() {console.log('func2');}
function func3() {console.log('func3');}
function func4() {console.log('func4');}
function func5() {console.log('func5');}

sub.on('click', func1);
sub.on('click', func2);
sub.on('click', func3);
sub.on('click', func4);
sub.on('click', func5);

sub.trigger('click');

sub.off('click', func3);
sub.off('click', func5);

sub.trigger('click');

function caculatePrice() {
  let sales = {
    "100-10": (price) => price -= 10,
    "200-25": (price) => price -= 25,
    "80%": (price) => price *= 0.8
  };

  function calculate(type, price) {
    if (!sales[type]) return "没有这个折扣";

    return sales[type](price);
  }

  calculate.add = (type, func) => {
    sales[type] = func;
  }

  calculate.del = (type) => {
    delete sales[type];
  }

  return calculate;
}

const calculate = caculatePrice();

const res = calculate('100-10', 300);
console.log(res);

const res2 = calculate('80%', 300);
console.log(res2);

const res3 = calculate('70%', 300);
console.log(res3);

calculate.add("70%", (price) => price *= 0.7);
const res4 = calculate('70%', 300);
console.log(res4);

calculate.del("80%");
const res5 = calculate('80%', 300);
console.log(res5);