JavaScript 创建真正的私有方法有什么缺点

根据其他编程语言如C++，Java等，私有方法是指不能与其他类共享，不能直接通过对象访问的方法。这个规则也适用于JavaScript。

所以首先我们要看看如何使用JavaScript创建私有方法？主要有四个关键字可以在类中创建私有方法：

var
let
const
#（哈希）
示例：

Javascript

<script> 
// class Geek 
  var Geek = function (article, published) { 
      // public member 
      this.programmingLang = "Js"; 
  
      // private member 
      var topic = "private_method"; 
      var status = published; 
  
      // private member function 
      var publish = () => { 
          console.log(article); 
          return status; 
      } 
  
      // calling private member  
      // function inside same class 
      console.log(publish()); 
  }; 
  
  // Geek1 is object of Geek class 
  var Geek1 = new Geek('ABC', 'YES'); 
  
  // calling public member outside the class 
  console.log(Geek1.programmingLang); 
<script/>

输出：

ABC
YES
Js

在JavaScript中创建真正的私有方法有两个主要的缺点。

无法在类外部调用私有方法。
当为同一个类创建不同的对象时，会产生内存效率问题，因为每个实例都会创建一个新的方法副本。

示例： 如果我们在类外部调用私有成员函数，那么会报错。

Javascript

<script> 
    var Geek = function (article, published) { 
        this.programmingLang = "Js"; 
        var topic = "private_method"; 
        var status = published; 
        var publish = () => { 
            console.log(article); 
            return status; 
        } 
        console.log(topic); 
    }; 
    var Geek1 = new Geek('ABC', 'YES'); 
    console.log(Geek1.programmingLang); 
    console.log(publish()); 
<script />

输出：

JavaScript 创建真正的私有方法有什么缺点

但是下面的例子会得到正确的输出：

Javascript

<script>   
  class A { 
      // Private field 
      #foo; 
      constructor(foo) { 
          this.#foo = "ABC"; 
      }
      #privateFun(prefix) { 
          return prefix + this.#foo; 
      } 
      publicFun() { 
          return this.#privateFun(">>"); 
      } 
  } 
  let a = new A(); 
  console.log(a.publicFun()); 
<script/>

输出:

>>ABC

示例： 如果我们为同一个类创建不同的对象，那么每个对象会为自己创建一个实例或者说复制该函数的实例。在这种情况下，会出现内存效率问题。

Javascript

<script> 
    var Employee = function (name, comp, sal) { 
        this.name = name; 
        this.company = comp; 
        this.salary = sal; 
  
        // Private method 
        var Sal_increase = () => { 
            this.salary = this.salary + 45000; 
        }; 
  
        // Public method 
        this.dispalySal = () => { 
            Sal_increase(); 
            console.log(this.salary); 
        }; 
    }; 
  
    const A = new Employee("A", "dream", 45000); 
    const B = new Employee("B", "young", 6000); 
    const C = new Employee("C", "inspire", 9000); 
  
    A.dispalySal() 
    B.dispalySal() 
    C.dispalySal() 
</script>

输出：