单例模式

var createSingle = （function() {
	var _flag = null
	return function () {
		if(_flag === null){
			_flag = true
		}
		return _flag
	}
}）()

var a1 = createSingle ()
var a2 = createSingle ()

console.log(a1 === a2)

工厂模式

 function A(name) {
      this.name = name
    }

    A.prototype.getName = function () {
      console.log(this.name)
    }

    function B(model) {
      this.model = model
    }

    B.prototype.getModel = function () {
      console.log(this.model)
    }


    function create(type, param) {
      // instanceof 会判断后面的构造函数的原型是否存在当前这个对象的原型链里
      if (this instanceof create) {
        return new this[type](param)
      } else {
        return new create(type, param)
      }

    }

    create.prototype = {
      A,
      B
    }

    var c = new create('A', '123')
    console.log(c); // A {name: '123'}
    var d = create("B", 666)
    console.log(d); // B { model: 666 }

策略模式

let strategy = {
	S:(salary) => {
		return salary*5
	},
	A:(salary) => {
		return salary*4
	},
	B:(salary) => {
		return salary*3
	},
	C:(salary) => {
		return salary*2
	},
}
function settlement(grade,salary){
	return strategy[grade](salary)
}
settlement('S',10000)  // 50000
settlement('A',5000) // 20000

发布订阅

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

    // 订阅事件
    on(event, listener) {
        if (!this.events[event]) {
            this.events[event] = [];
        }
        this.events[event].push(listener);
    }

    // 发布事件
    emit(event, ...args) {
        if (this.events[event]) {
            this.events[event].forEach(listener => {
                listener(...args);
            });
        }
    }

    // 移除事件监听器
    off(event, listener) {
        if (this.events[event]) {
            this.events[event] = this.events[event].filter(l => l !== listener);
        }
    }

    // 只订阅一次事件
    once(event, listener) {
        const onceListener = (...args) => {
            listener(...args);
            this.off(event, onceListener);
        };
        this.on(event, onceListener);
    }
}

// 使用示例
const emitter = new EventEmitter();

// 订阅事件
emitter.on('greet', (name) => {
    console.log(`Hello, ${name}!`);
});

// 发布事件
emitter.emit('greet', 'Alice'); // 输出: Hello, Alice!

// 移除事件监听器
const listener = (name) => {
    console.log(`Goodbye, ${name}!`);
};
emitter.on('greet', listener);
emitter.off('greet', listener);

// 只订阅一次事件
emitter.once('greet', (name) => {
    console.log(`Hi, ${name}!`);
});
emitter.emit('greet', 'Bob'); // 输出: Hi, Bob!
emitter.emit('greet', 'Charlie'); // 不会输出任何内容