JavaScript私有方法

Question

要使用公共方法创建JavaScript类,我会执行以下操作:

function Restaurant() {}

Restaurant.prototype.buy_food = function(){
   // something here
}

Restaurant.prototype.use_restroom = function(){
   // something here
}

这样我班级的用户可以:

var restaurant = new Restaurant();
restaurant.buy_food();
restaurant.use_restroom();

如何创建一个可由buy_food和use_restroom方法调用的私有方法,但不能由类的用户创建外部方法？

换句话说,我希望我的方法实现能够:

Restaurant.prototype.use_restroom = function() {
   this.private_stuff();
}

但这不应该奏效:

var r = new Restaurant();
r.private_stuff();

我如何定义private_stuff为私有方法,所以这两个都适用？

我已经阅读了Doug Crockford的几次写法,但看起来似乎不能通过公共方法调用"私有"方法,并且可以在外部调用"特权"方法.

Answer 1

你可以做到,但缺点是它不能成为原型的一部分:

function Restaurant() {
    var myPrivateVar;

    var private_stuff = function() {  // Only visible inside Restaurant()
        myPrivateVar = "I can set this here!";
    }

    this.use_restroom = function() {  // use_restroom is visible to all
        private_stuff();
    }

    this.buy_food = function() {   // buy_food is visible to all
        private_stuff();
    }
}

Answer 2

你可以像这样模拟私有方法:

function Restaurant() {
}

Restaurant.prototype = (function() {
    var private_stuff = function() {
        // Private code here
    };

    return {

        constructor:Restaurant,

        use_restroom:function() {
            private_stuff();
        }

    };
})();

var r = new Restaurant();

// This will work:
r.use_restroom();

// This will cause an error:
r.private_stuff();

有关此技术的更多信息,请访问:http://webreflection.blogspot.com/2008/04/natural-javascript-private-methods.html

Answer 3

使用自调用功能和调用

JavaScript使用原型,并且没有像面向对象语言那样的类(或方法).JavaScript开发人员需要在JavaScript中思考.

维基百科报价:

与许多面向对象的语言不同,函数定义和方法定义之间没有区别.相反,区别发生在函数调用期间; 当一个函数作为一个对象的方法被调用时,该函数的local this关键字被绑定到该调用的该对象.

解决方案使用自调用函数和调用函数来调用私有"方法":

var MyObject = (function () {

    // Constructor
    function MyObject (foo) {
        this._foo = foo;
    }

    function privateFun (prefix) {
        return prefix + this._foo;
    }

    MyObject.prototype.publicFun = function () {
        return privateFun.call(this, '>>');
    }

    return MyObject;
})();


var myObject = new MyObject('bar');
myObject.publicFun();      // Returns '>>bar'
myObject.privateFun('>>'); // ReferenceError: private is not defined

该呼叫功能可以让我们调用私有函数与适当的上下文(this).

使用Node.js更简单

如果您使用的是node.js,则不需要IIFE,因为您可以利用模块加载系统:

function MyObject (foo) {
    this._foo = foo;
}

function privateFun (prefix) {
    return prefix + this._foo;
}

MyObject.prototype.publicFun = function () {
    return privateFun.call(this, '>>');
}

exports.MyObject = MyObject;

加载文件:

var MyObject = require('./MyObject').MyObject;

var myObject = new MyObject('bar');
myObject.publicFun();      // Returns '>>bar'
myObject.privateFun('>>'); // ReferenceError: private is not defined

(实验)ES7与绑定操作员

绑定运算符::是ECMAScript 提议,在Babel(阶段0)中实现.

export default class MyObject {
  constructor (foo) {
    this._foo = foo;
  }

  publicFun () {
    return this::privateFun('>>');
  }
}

function privateFun (prefix) {
  return prefix + this._foo;
}

加载文件:

import MyObject from './MyObject';

let myObject = new MyObject('bar');
myObject.publicFun();      // Returns '>>bar'
myObject.privateFun('>>'); // TypeError: myObject.privateFun is not a function

Answer 4

在这种情况下,如果你有一个公共API,并且你想要私有和公共方法/属性,我总是使用模块模式.这个模式在YUI库中很流行,详情可以在这里找到:

http://yuiblog.com/blog/2007/06/12/module-pattern/

这非常简单,其他开发人员也很容易理解.举个简单的例子:

var MYLIB = function() {  
    var aPrivateProperty = true;
    var aPrivateMethod = function() {
        // some code here...
    };
    return {
        aPublicMethod : function() {
            aPrivateMethod(); // okay
            // some code here...
        },
        aPublicProperty : true
    };  
}();

MYLIB.aPrivateMethod() // not okay
MYLIB.aPublicMethod() // okay

Answer 5

这是我创建的类,用于理解Douglas Crockford在其JavaScript站点中的私人成员所建议的内容

function Employee(id, name) { //Constructor
    //Public member variables
    this.id = id;
    this.name = name;
    //Private member variables
    var fName;
    var lName;
    var that = this;
    //By convention, we create a private variable 'that'. This is used to     
    //make the object available to the private methods. 

    //Private function
    function setFName(pfname) {
        fName = pfname;
        alert('setFName called');
    }
    //Privileged function
    this.setLName = function (plName, pfname) {
        lName = plName;  //Has access to private variables
        setFName(pfname); //Has access to private function
        alert('setLName called ' + this.id); //Has access to member variables
    }
    //Another privileged member has access to both member variables and private variables
    //Note access of this.dataOfBirth created by public member setDateOfBirth
    this.toString = function () {
        return 'toString called ' + this.id + ' ' + this.name + ' ' + fName + ' ' + lName + ' ' + this.dataOfBirth; 
    }
}
//Public function has access to member variable and can create on too but does not have access to private variable
Employee.prototype.setDateOfBirth = function (dob) {
    alert('setDateOfBirth called ' + this.id);
    this.dataOfBirth = dob;   //Creates new public member note this is accessed by toString
    //alert(fName); //Does not have access to private member
}
$(document).ready()
{
    var employee = new Employee(5, 'Shyam'); //Create a new object and initialize it with constructor
    employee.setLName('Bhaskar', 'Ram');  //Call privileged function
    employee.setDateOfBirth('1/1/2000');  //Call public function
    employee.id = 9;                     //Set up member value
    //employee.setFName('Ram');  //can not call Private Privileged method
    alert(employee.toString());  //See the changed object

}

Answer 6

我想到了这个:编辑:实际上,有人已经链接到相同的解决方案.咄!

var Car = function() {
}

Car.prototype = (function() {
    var hotWire = function() {
        // Private code *with* access to public properties through 'this'
        alert( this.drive() ); // Alerts 'Vroom!'
    }

    return {
        steal: function() {
            hotWire.call( this ); // Call a private method
        },
        drive: function() {
            return 'Vroom!';
        }
    };
})();

var getAwayVechile = new Car();

hotWire(); // Not allowed
getAwayVechile.hotWire(); // Not allowed
getAwayVechile.steal(); // Alerts 'Vroom!'

Answer 7

您现在可以使用es10 私有方法执行此操作。您只需要#在方法名称前添加一个。

class ClassWithPrivateMethod {
  #privateMethod() {
    return 'hello world';
  }

  getPrivateMessage() {
    return #privateMethod();
  }
}

Answer 8

我认为这些问题一次又一次地出现,因为对闭包缺乏了解.Сlosures是JS中最重要的事情.每个JS程序员都必须感受到它的本质.

1.首先我们需要独立的范围(关闭).

function () {

}

2.在这方面,我们可以做任何我们想做的.没有人会知道它.

function () {
    var name,
        secretSkills = {
            pizza: function () { return new Pizza() },
            sushi: function () { return new Sushi() }
        }

    function Restaurant(_name) {
        name = _name
    }
    Restaurant.prototype.getFood = function (name) {
        return name in secretSkills ? secretSkills[name]() : null
    }
}

3.为了让全世界了解我们的餐厅类,我们必须从封闭处归还.

var Restaurant = (function () {
    // Restaurant definition
    return Restaurant
})()

4.最后,我们有:

var Restaurant = (function () {
    var name,
        secretSkills = {
            pizza: function () { return new Pizza() },
            sushi: function () { return new Sushi() }
        }

    function Restaurant(_name) {
        name = _name
    }
    Restaurant.prototype.getFood = function (name) {
        return name in secretSkills ? secretSkills[name]() : null
    }
    return Restaurant
})()

5.此外,该方法对于继承和模板潜力

// Abstract class
function AbstractRestaurant(skills) {
    var name
    function Restaurant(_name) {
        name = _name
    }
    Restaurant.prototype.getFood = function (name) {
        return skills && name in skills ? skills[name]() : null
    }
    return Restaurant
}

// Concrete classes
SushiRestaurant = AbstractRestaurant({ 
    sushi: function() { return new Sushi() } 
})

PizzaRestaurant = AbstractRestaurant({ 
    pizza: function() { return new Pizza() } 
})

var r1 = new SushiRestaurant('Yo! Sushi'),
    r2 = new PizzaRestaurant('Dominos Pizza')

r1.getFood('sushi')
r2.getFood('pizza')

我希望这有助于人们更好地理解这个主题

Answer 9

就个人而言,我更喜欢以下模式在JavaScript中创建类:

var myClass = (function() {
    // Private class properties go here

    var blueprint = function() {
        // Private instance properties go here
        ...
    };

    blueprint.prototype = { 
        // Public class properties go here
        ...
    };

    return  {
         // Public class properties go here
        create : function() { return new blueprint(); }
        ...
    };
})();

如您所见,它允许您定义类属性和实例属性,每个属性都可以是公共属性和私有属性.

演示

var Restaurant = function() {
    var totalfoodcount = 0;        // Private class property
    var totalrestroomcount  = 0;   // Private class property
    
    var Restaurant = function(name){
        var foodcount = 0;         // Private instance property
        var restroomcount  = 0;    // Private instance property
        
        this.name = name
        
        this.incrementFoodCount = function() {
            foodcount++;
            totalfoodcount++;
            this.printStatus();
        };
        this.incrementRestroomCount = function() {
            restroomcount++;
            totalrestroomcount++;
            this.printStatus();
        };
        this.getRestroomCount = function() {
            return restroomcount;
        },
        this.getFoodCount = function() {
            return foodcount;
        }
    };
   
    Restaurant.prototype = {
        name : '',
        buy_food : function(){
           this.incrementFoodCount();
        },
        use_restroom : function(){
           this.incrementRestroomCount();
        },
        getTotalRestroomCount : function() {
            return totalrestroomcount;
        },
        getTotalFoodCount : function() {
            return totalfoodcount;
        },
        printStatus : function() {
           document.body.innerHTML
               += '<h3>Buying food at '+this.name+'</h3>'
               + '<ul>' 
               + '<li>Restroom count at ' + this.name + ' : '+ this.getRestroomCount() + '</li>'
               + '<li>Food count at ' + this.name + ' : ' + this.getFoodCount() + '</li>'
               + '<li>Total restroom count : '+ this.getTotalRestroomCount() + '</li>'
               + '<li>Total food count : '+ this.getTotalFoodCount() + '</li>'
               + '</ul>';
        }
    };

    return  { // Singleton public properties
        create : function(name) {
            return new Restaurant(name);
        },
        printStatus : function() {
          document.body.innerHTML
              += '<hr />'
              + '<h3>Overview</h3>'
              + '<ul>' 
              + '<li>Total restroom count : '+ Restaurant.prototype.getTotalRestroomCount() + '</li>'
              + '<li>Total food count : '+ Restaurant.prototype.getTotalFoodCount() + '</li>'
              + '</ul>'
              + '<hr />';
        }
    };
}();

var Wendys = Restaurant.create("Wendy's");
var McDonalds = Restaurant.create("McDonald's");
var KFC = Restaurant.create("KFC");
var BurgerKing = Restaurant.create("Burger King");

Restaurant.printStatus();

Wendys.buy_food();
Wendys.use_restroom();
KFC.use_restroom();
KFC.use_restroom();
Wendys.use_restroom();
McDonalds.buy_food();
BurgerKing.buy_food();

Restaurant.printStatus();

BurgerKing.buy_food();
Wendys.use_restroom();
McDonalds.buy_food();
KFC.buy_food();
Wendys.buy_food();
BurgerKing.buy_food();
McDonalds.buy_food();

Restaurant.printStatus();

另见这个小提琴.

Answer 10

所有这些关闭将花费你.确保测试速​​度影响,尤其是在IE中.您会发现最好使用命名约定.还有很多企业网站用户被迫使用IE6 ......

Answer 11

别这么啰嗦。它是 JavaScript。使用命名约定。

在 es6 类工作多年后，我最近开始研究一个 es5 项目（使用已经很冗长的 requireJS）。我已经一遍又一遍地提到这里提到的所有策略，基本上都归结为使用命名约定：

1. Javascript 没有像private. 其他使用 Javascript 的开发人员会预先知道这一点。因此，一个简单的命名约定就足够了。下划线前缀的简单命名约定解决了私有属性和私有方法的问题。
2. 出于速度原因，让我们利用 Prototype，但不要再冗长了。让我们尽量让 es5 “类”看起来尽可能接近我们在其他后端语言中的预期（并将每个文件视为一个类，即使我们不需要返回一个实例）。
3. 让我们用一个更现实的模块情况来演示（我们将使用旧的 es5 和旧的 requireJs）。

我的工具提示.js

    define([
        'tooltip'
    ],
    function(
        tooltip
    ){

        function MyTooltip() {
            // Later, if needed, we can remove the underscore on some
            // of these (make public) and allow clients of our class
            // to set them.
            this._selector = "#my-tooltip"
            this._template = 'Hello from inside my tooltip!';
            this._initTooltip();
        }

        MyTooltip.prototype = {
            constructor: MyTooltip,

            _initTooltip: function () {
                new tooltip.tooltip(this._selector, {
                    content: this._template,
                    closeOnClick: true,
                    closeButton: true
                });
            }
        }

        return {
            init: function init() {
               new MyTooltip();  // <-- Our constructor adds our tooltip to the DOM so not much we need to do after instantiation.
            }

            // You could instead return a new instantiation, 
            // if later you do more with this class.
            /* 
            create: function create() {
               return new MyTooltip();
            }
            */
        }
    });

Answer 12

ES2021 / ES12 - 私有方法

私有方法名称以哈希#前缀开头，并且只能在定义它的类中访问。

class Restaurant {

  // private method
  #private_stuff() {
    console.log("private stuff");
  }

  // public method
  buy_food() {
    this.#private_stuff();
  }

};

const restaurant = new Restaurant();
restaurant.buy_food(); // "private stuff";
restaurant.private_stuff(); // Uncaught TypeError: restaurant.private_stuff is not a function