Question

我有一个名为 bank 的对象，当用户存入例如 50 欧元时，余额始终为 0。老实说，我不明白为什么？我的方法 deposit() 不正确？

var bank = {
    name : "Depuis",
    firstname : "Denis",
    accountNumber : "BE42-1525899822",
    email : "depuis.denisf@gmail.com",
    phone : "010.49.48.00",
    balance : 0.0
};


deposit(50);
console.log("Balance is of => " + bank.balance);

function deposit(amount){
    if(amount > 0){
        this.balance += amount;
        console.log("The amount is of " + amount + " euros.");
    }
}

Answer 1

您应该考虑如何使用 this 运算符。在此网站中，您可以搜索更多信息：https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this

查看下一个示例：

const test = {
  prop: 42,
  func: function() {
    return this.prop;
  },
};

console.log(test.func());
// expected output: 42

在此代码示例中使用了 function 关键字，因此 this 关键字可用于访问对象字段。你应该考虑到它内部调用的每个函数都可以使用 this 操作符来获取相同的对象引用。

Answer 2

this 内部的存款函数不是指bank 对象，而是指window 对象，这是因为该函数的调用方式。

>

您可以在银行对象中添加一个方法，该方法可以调用 deposit 函数，该函数将使 this 引用银行对象。

this 是根据上下文设置的。在下面的代码段中，deposit 函数以类似的方式被调用，但来自不同的上下文，它以不同的方式设置 this。

您应该阅读评论中提到的有关 this 如何工作的更多信息。

var bank = {
    name : "Depuis",
    firstname : "Denis",
    accountNumber : "BE42-1525899822",
    email : "depuis.denisf@gmail.com",
    phone : "010.49.48.00",
    balance : 0.0,
    depositAmt: function(amount) {
      deposit(amount)
    }
};

bank.depositAmt(50);
console.log("Balance is of => " + bank.balance);

function deposit(amount){
    if(amount > 0){
        // this now refers to the bank object
        this.balance += amount;
        console.log("The amount is of " + amount + " euros.");
    }
}

或者你可以直接引用 bank 对象。

var bank = {
    name : "Depuis",
    firstname : "Denis",
    accountNumber : "BE42-1525899822",
    email : "depuis.denisf@gmail.com",
    phone : "010.49.48.00",
    balance : 0.0
};


deposit(50);
console.log("Balance is of => " + bank.balance);

function deposit(amount){
    if(amount > 0){
        // this here does not refer to that 
        // it refers to the window
        bank.balance += amount;
        console.log("The amount is of " + amount + " euros.");
    }
}

Answer 3

您需要调用该函数并将上下文设置为 bank。

const bank = {
  name: "Depuis",
  firstname: "Denis",
  accountNumber: "BE42-1525899822",
  email: "depuis.denisf@gmail.com",
  phone: "010.49.48.00",
  balance: 0.0
};

deposit.call(bank, 50); // Call with context of the bank.
console.log(`Current balance: ${bank.balance} euros`);

function deposit(amount) {
  if (amount > 0) {
    this.balance += amount;
    console.log(`The amount is of ${amount} euros.`);
  }
}

更好的替代方法是使用 OOP 并创建一个可以访问和修改帐户余额的 Bank 对象。

const main = () => {
  const bank = new Bank({ currencyType: '€' });
  const customer = bank.createCustomer({
    givenName: "Denis",
    surname: "Depuis",
    email: "depuis.denisf@gmail.com",
    phone: "010.49.48.00"
  });
  const { accountNumber } = customer;

  console.log(customer.greeting());
  bank.deposit(accountNumber, 50.25);
  bank.withdraw(accountNumber, 20.10);
};

const defaultCustomerProperties = {
  givenName: '',
  surname: '',
  email: '',
  phone: '',
  balance: 0.00
};

class Customer {
  constructor(options) {
    const opts = { ...defaultCustomerProperties, ...options };
    this.accountNumber = opts.accountNumber;
    this.givenName = opts.givenName;
    this.surname = opts.surname;
    this.email = opts.email;
    this.phone = opts.phone;
    this.balance = opts.balance;
  }
  greeting() {
    return `Welcome ${this.givenName}! (${this.accountNumber})`;
  }
}

class Bank {
  constructor(options = {}) {
    this.currencyType = options.currencyType || '$';
    this.customers = {};
  }
  createCustomer(options) {
    const accountNumber = `BExx-xxxxxxxxxx`.replace(/x/g, g => Math.floor(Math.random() * 10));
    const account = new Customer({ ...options, accountNumber });
    this.customers[accountNumber] = account;
    return account;
  }
  findCustomer(accountId) {
    const customer = this.customers[accountId];
    if (customer == null) {
      throw new Error(`Account by [id=${accountId}] not found!`);
    }
    return customer;
  }
  deposit(accountId, amount) {
    const customer = this.findCustomer(accountId);
    customer.balance += amount;
    console.log(`Deposited ${this.formatCurrency(amount)} into ${accountId}. New balance: ${this.formatCurrency(customer.balance)}`);
  }
  withdraw(accountId, amount) {
    const customer = this.findCustomer(accountId);
    if (customer.balance < amount) {
      throw new Error(`Customer balance is less than the desired amount!`);
    }
    customer.balance -= amount;
    console.log(`Withdrew ${this.formatCurrency(amount)} from ${accountId}. New balance: ${this.formatCurrency(customer.balance)}`);
  }
  formatCurrency(amount) {
    return `${this.currencyType}${amount.toFixed(2)}`;
  }
  retrieveBalance(accountId) {
    const customer = this.findCustomer(accountId);
    return customer.balance;
  }
};

main();

.as-console-wrapper { top: 0; max-height: 100% !important; }

一次存款后计算金额的方法

3 个答案: