有问题在ES6类中创建静态字段（非方法，基元）？

Question

我想创建一个BankAccount类，其中新实例跟踪新实例的检查和节省。然而，每当有人创建一个新实例时，我想要一个静态方法，它调用一个静态字段，该字段仅与BankAccount类相关，该类可以跟踪有多少银行帐户已打开（有点像单例行为）。这在c＃/ java中是可行的，但很难在Javascript中重新创建预期的行为。

我在ES5尝试这很好，但短了，我来我一直在寻找使用功能的包装来封装行为最接近的事：

function BankAccountMaker() { 
    var countOfAccounts = 0; 
    function IncrementcountOfAccounts() { 
     countOfAccounts += 1; 
    } 

    function BankAccount(c = 0) { 
     this.checking = 0; 
    } 

    return { 
     makeBankAccount: function (c) { 
      IncrementcountOfAccounts(); 
      console.log(countOfAccounts) 
      return new BankAccount(c); 
     } 
    } 
} 

最终，几个要求：

1. 有人可以编码ES6相当于上述？
2. 另外，有没有更好的方法来做到这一点在ES5中，我不需要包装？
3. 在ES5中，我们可以将原型方法设置为原语，但似乎并不像ES6语法那样呢？ （我正在使用Node 6.1和Babel fwiw）

Answer 1

我已经为每个银行帐户添加了一个id。所以你可以遍历你创建的账户。 incrementcountAccounts是一个坏主意，因为你不知道银行账户是否真的被创建。

您不能这样做：BankAccount(c = 0)参数在ES5中不受支持。

一些片段：

/** 
 
* Bank 
 
*/ 
 
class Bank { 
 
    constructor(name, id) { 
 
    this.countOfAccounts = 0; 
 
    this.id = id; 
 
    this.name = name; 
 
    
 
    console.log('--- ' + this.name + ' ---'); 
 
    } 
 

 
    incrementcountOfAccounts() { 
 
    this.countOfAccounts += 1; 
 
    } 
 
    
 
    addBankAccount(...data) { 
 
    this.incrementcountOfAccounts(); 
 
    
 
    return new BankAccount(this.id, ...data); 
 
    } 
 
} 
 

 
/** 
 
* BankAccount 
 
*/ 
 
class BankAccount { 
 
    /** 
 
    * Constrctor 
 
    * @param {Number} bankId  
 
    * @param {Number} [amount=0] 
 
    * @param {Number} [checking=0]    
 
    */ 
 
    constructor(bankId, amount = 0, checking = 0) { 
 
    if(!bankId) { 
 
     throw Error('no bank id'); 
 
    } 
 
    
 
    this.account = { 
 
     bankId, 
 
     checking, 
 
     amount 
 
    }; 
 
    } 
 
    
 
    /** 
 
    * Get bank id 
 
    * @return {number} 
 
    */ 
 
    get bankId() { 
 
    return this.account.bankId; 
 
    } 
 

 
    /** 
 
    * Set amount 
 
    * @param {number} value 
 
    * @return {number}  
 
    */ 
 
    set amount(value) { 
 
    this.account.amount = value; 
 
    } 
 

 
    /** 
 
    * Get ammunt 
 
    * @return {number} 
 
    */ 
 
    get amount() { 
 
    return this.account.amount; 
 
    } 
 

 
    /** 
 
    * set checking 
 
    * @param {number} value 
 
    * @return {number}  
 
    */ 
 
    set checking(value) { 
 
    this.account.checking = value; 
 
    } 
 

 
    /** 
 
    * get checking 
 
    * @return {number} 
 
    */ 
 
    get checking() { 
 
    return this.account.checking; 
 
    } 
 
} 
 

 
const FirstBank = new Bank('First Bank', 1); 
 

 

 
const bankAccount1 = FirstBank.addBankAccount(300); 
 
const bankAccount2 = FirstBank.addBankAccount(4000); 
 

 

 
console.log('Account 1: ' + bankAccount1.amount + ' - ' + bankAccount1.checking + ' - ' + bankAccount1.bankId); 
 
console.log('Account 2: ' + bankAccount2.amount + ' - ' + bankAccount1.checking + ' - ' + bankAccount1.bankId); 
 

 

 
console.log('Accounts first Bank: ' + FirstBank.countOfAccounts); 
 

 
const SecondBank = new Bank('Second Bank', 4); 
 
const bankAccount3 = SecondBank.addBankAccount(0, 1); 
 
console.log('Account 3: ' + bankAccount3.amount + ' - ' + bankAccount1.checking + ' - ' + bankAccount1.bankId);  
 
console.log('Accounts second Bank: ' + SecondBank.countOfAccounts);

ES5：

var BankAccountMaker = function() { 
 
    this.countOfAccounts = 0; 
 
    
 
    this.IncrementcountOfAccounts = function() { 
 
    this.countOfAccounts += 1; 
 
    } 
 
    
 
    this.BankAccount = function() { 
 
    this.checking = 0; 
 
    } 
 
    
 
    this.makeBankAccount = function (c) { 
 
    this.IncrementcountOfAccounts(); 
 

 
    return new this.BankAccount(c); 
 
    } 
 
} 
 

 
const Bank = new BankAccountMaker(); 
 

 
console.log(Bank.makeBankAccount(3)); 
 
console.log(Bank.makeBankAccount(3)); 
 
console.log(Bank.makeBankAccount(3)); 
 
console.log(Bank.countOfAccounts);

ES5原型：

function BankAccountMaker() { 
 
    this.countOfAccounts = 0; 
 

 
} 
 

 
BankAccountMaker.prototype.IncrementcountOfAccounts = function() { 
 
    this.countOfAccounts += 1; 
 
} 
 

 
BankAccountMaker.prototype.BankAccount = function() { 
 
    this.checking = 0; 
 
} 
 

 
BankAccountMaker.prototype.IncrementcountOfAccounts = function() { 
 
    this.countOfAccounts += 1; 
 
} 
 

 
BankAccountMaker.prototype.makeBankAccount = function(c) { 
 
    this.IncrementcountOfAccounts(); 
 
    console.log(this.countOfAccounts); 
 
    
 
    return new this.BankAccount(c); 
 
} 
 

 
const Bank = new BankAccountMaker(); 
 

 
console.log(Bank.makeBankAccount(3)); 
 
console.log(Bank.makeBankAccount(3)); 
 
console.log(Bank.makeBankAccount(3)); 
 
console.log(Bank.countOfAccounts);