是否可以在ES6类中创建私有属性?

举个例子。 如何阻止访问instance.property?

class Something {
  constructor(){
    this.property = "test";
  }
}

var instance = new Something();
console.log(instance.property); //=> "test"

当前回答

哦,这么多奇异的解决方案!我通常不关心隐私,所以我使用“伪隐私”,正如这里所说的。但如果确实关心(如果有一些特殊的要求),我会在这个例子中使用:

class jobImpl{
  // public
  constructor(name){
    this.name = name;
  }
  // public
  do(time){
    console.log(`${this.name} started at ${time}`);
    this.prepare();
    this.execute();
  }
  //public
  stop(time){
    this.finish();
    console.log(`${this.name} finished at ${time}`);
  }
  // private
  prepare(){ console.log('prepare..'); }
  // private
  execute(){ console.log('execute..'); }
  // private
  finish(){ console.log('finish..'); }
}

function Job(name){
  var impl = new jobImpl(name);
  return {
    do: time => impl.do(time),
    stop: time => impl.stop(time)
  };
}

// Test:
// create class "Job"
var j = new Job("Digging a ditch");
// call public members..
j.do("08:00am");
j.stop("06:00pm");

// try to call private members or fields..
console.log(j.name); // undefined
j.execute(); // error

函数(构造函数)的另一种可能实现:

function Job(name){
  var impl = new jobImpl(name);
  this.do = time => impl.do(time),
  this.stop = time => impl.stop(time)
}

其他回答

大多数答案要么说不可能,要么要求你使用WeakMap或Symbol,这是ES6的特性,可能需要腻子。然而,还有另一种方法!看看这个:

// 1. Create closure var SomeClass = function() { // 2. Create `key` inside a closure var key = {}; // Function to create private storage var private = function() { var obj = {}; // return Function to access private storage using `key` return function(testkey) { if(key === testkey) return obj; // If `key` is wrong, then storage cannot be accessed console.error('Cannot access private properties'); return undefined; }; }; var SomeClass = function() { // 3. Create private storage this._ = private(); // 4. Access private storage using the `key` this._(key).priv_prop = 200; }; SomeClass.prototype.test = function() { console.log(this._(key).priv_prop); // Using property from prototype }; return SomeClass; }(); // Can access private property from within prototype var instance = new SomeClass(); instance.test(); // `200` logged // Cannot access private property from outside of the closure var wrong_key = {}; instance._(wrong_key); // undefined; error logged

我称这个方法为accessor pattern。基本思想是我们有一个闭包,闭包中有一个键,我们创建一个私有对象(在构造函数中),只有当你拥有键时才能访问它。

如果你感兴趣,你可以在我的文章中阅读更多有关这方面的内容。使用此方法,可以为每个对象创建不能在闭包外部访问的属性。因此,你可以在构造函数或原型中使用它们,但不能在其他任何地方使用。我还没有在任何地方见过这种方法,但我认为它真的很强大。

另一种方式类似于上两个帖子

class Example {
  constructor(foo) {

    // privates
    const self = this;
    this.foo = foo;

    // public interface
    return self.public;
  }

  public = {
    // empty data
    nodata: { data: [] },
    // noop
    noop: () => {},
  }

  // everything else private
  bar = 10
}

const test = new Example('FOO');
console.log(test.foo); // undefined
console.log(test.noop); // { data: [] }
console.log(test.bar); // undefined

哦,这么多奇异的解决方案!我通常不关心隐私,所以我使用“伪隐私”,正如这里所说的。但如果确实关心(如果有一些特殊的要求),我会在这个例子中使用:

class jobImpl{
  // public
  constructor(name){
    this.name = name;
  }
  // public
  do(time){
    console.log(`${this.name} started at ${time}`);
    this.prepare();
    this.execute();
  }
  //public
  stop(time){
    this.finish();
    console.log(`${this.name} finished at ${time}`);
  }
  // private
  prepare(){ console.log('prepare..'); }
  // private
  execute(){ console.log('execute..'); }
  // private
  finish(){ console.log('finish..'); }
}

function Job(name){
  var impl = new jobImpl(name);
  return {
    do: time => impl.do(time),
    stop: time => impl.stop(time)
  };
}

// Test:
// create class "Job"
var j = new Job("Digging a ditch");
// call public members..
j.do("08:00am");
j.stop("06:00pm");

// try to call private members or fields..
console.log(j.name); // undefined
j.execute(); // error

函数(构造函数)的另一种可能实现:

function Job(name){
  var impl = new jobImpl(name);
  this.do = time => impl.do(time),
  this.stop = time => impl.stop(time)
}

更新:一个语法更好的提案正在酝酿中。欢迎投稿。


是的,对于对象的作用域访问,ES6引入了符号。

符号是唯一的,你不能从外部访问一个,除非通过反射(就像Java/ c#中的私有),但任何有权访问内部符号的人都可以使用它进行键访问:

var property = Symbol();
class Something {
    constructor(){
        this[property] = "test";
    }
}

var instance = new Something();

console.log(instance.property); //=> undefined, can only access with access to the Symbol

你可以试试这个https://www.npmjs.com/package/private-members

这个包将按实例保存成员。

const pvt = require('private-members');
const _ = pvt();

let Exemplo = (function () {    
    function Exemplo() {
        _(this).msg = "Minha Mensagem";
    }

    _().mensagem = function() {
        return _(this).msg;
    }

    Exemplo.prototype.showMsg = function () {
        let msg = _(this).mensagem();
        console.log(msg);
    };

    return Exemplo;
})();

module.exports = Exemplo;