前端设计模式

工厂模式(Factory pattern)

解决了创建多个相似对象的问题,但却没有体现对象类型

function createPerson(name, age, job) {
  let o = {}
  o.name = name
  o.age = age
  o.job = job
  o.sayName = function () {
    console.log(name)
  }
  return o
}
var person1 = createPerson('mamba', 24, 'Software Engineer')
var person2 = createPerson('hui', 20, 'Doctor')

构造函数模式(Constructor pattern)

function Person(name, age) {
  this.name = name
  this.age = age
}
Person.prototype.sayName = function () {
  console.log(this.name)
}

let person1 = new Person('mamba', 24)

混合模式(Mixin pattern)

function object(o) {
  function F() {}
  F.prototype = o
  return new F()
}

function inheritPrototype(subType, superType) {
  var prototype = superType.prototype
  prototype.constructor = subType
  subType.prototype = prototype
}

function Person(name, age) {
  this.name = name
  this.age = age
}
Person.prototype.sayName = function () {
  console.log(this.name)
}

function Student(name, age, score) {
  Person.call(this, name, age)
  this.score = score
}
inheritPrototype(Student, Person)
Student.prototype.sayScore = function () {
  console.log(this.score)
}

模块模式与单例模式(module and singleton)

单例就是保证一个类只有一个实例,实现的方法一般是先判断实例存在与否,如果存在直接返回,如果不存在就创建了再返回,这就确保了一个类只有一个实例对象。

在JavaScript里,实现单例的方式有很多种,其中最简单的一个方式是使用对象字面量的方法,其字面量里可以包含大量的属性和方法:

var mySingleton = {
    property1: "something",
    property2: "something else",
    method1: function () {
        console.log('hello world');
    }
};

如果以后要扩展该对象,你可以添加自己的私有成员和方法,然后使用闭包在其内部封装这些变量和函数声明。只暴露你想暴露的public成员和方法,这就是模块模式,样例代码如下:

var mySingleton = (function () {

    /* 这里声明私有变量和方法 */
    var privateVariable = 'something private';
    function showPrivate() {
        console.log(privateVariable);
    }

    /* 公有变量和方法(可以访问私有变量和方法) */
    return {
        publicMethod: function () {
            showPrivate();
        },
        publicVar: 'the public can see this!'
    };
})();

继续对单利进行改进,我们想做到只有在使用的时候才初始化,那该如何做呢?如下:

let singleton = (function () {
  let instance
  function init(name) {
    
    /*这里定义单例代码,定义私有成员*/
    let prefixer = 'mamba-'
    
    return {
      /*这里定义共有成员*/
      getName: function () {
        console.log(prefixer + name)
      }
    }
  }
  return {
    getInstance: function (name) {
      if(!instance) {
        instance = init(name)
      }
      return instance
    }
  }
})()

singleton.getInstance('hui').getName()   // mamba-hui
singleton.getInstance('he').getName()    // mamba-hui 

发布订阅模式(Publish/Subscribe Pattern)

function EventTarget() {
  this.handlers = {}
}

EventTarget.prototype = {
  constructor: EventTarget,
  //添加事件
  addHandler: function (type, handler) {
    this.handlers[type] = this.handlers[type] || []
    this.handlers[type].push(handler)
  },
  //触发事件
  fire: function (event) {
    if (Array.isArray(this.handlers[event.type])) {
      let handlers = this.handlers[event.type]
      handlers.forEach((handle) => {
        console.log(this)
        handle.call(this, event)
      })
    }
  },
  // 取消订阅
  removeHandler: function (type, handler) {
    if (Array.isArray(this.handlers[type])) {
      let handlers = this.handlers[type]
      for (let i = 0; i < handlers.length; i++) {
        if (handlers[i] === handler) {
          handlers.splice(i, 1)
          break
        }
      }
    }
  }
}

let eventObj = new EventTarget()
let handler = () => {
  console.dir('何文会是哈哈哈哈')
}
eventObj.addHandler('alert', handler)
eventObj.fire({type: 'alert'})
eventObj.fire({type: 'alert'})
eventObj.removeHandler('alert', handler)
eventObj.fire({type: 'alert'})

// 事件继承
let object = function (o) {
  function F() {}
  F.prototype = o
  return new F()
}

let inheritPrototype = function (subType, superType) {
  let protopype = object(superType.prototype)
  protopype.constructor = subType
  subType.prototype = protopype
}

function Person(name, age) {
  EventTarget.call(this)
  this.name = name
  this.age = age
}

inheritPrototype(Person, EventTarget)

Person.prototype.say = function (message) {
  this.fire({
    type: 'message',
    message: message
  })
}

let handMessage = function (event) {
  console.dir(this.name + 'say: ' + event.message)
}

let person = new Person('yhlp', 29)
person.addHandler('message', handMessage)
person.say('Hi, there')

使用发布订阅模式写一个事件管理器

let Event = (function () {
  let events = {}
  function on(type, handle) {
    events[type] = events[type] || []
    events[type].push(handle)
  }
  function fire(type, ...args) {
    if(Array.isArray(events[type])) {
      events[type].forEach((item) => {
        item.apply(this, args)
      })
    }
  }
  function off(type) {
    events[type] && delete events[type]
  }
  return {
    on: on,
    fire: fire,
    off: off
  }
})()


Event.on('change', function(val){
  console.log('change...  now val is ' + val);
});
Event.fire('change', '饥人谷');
Event.off('changer');

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