如何返回對象數組屬性的總和而不是它們的double？

Question

我正在制作一個費用跟蹤器的基本代碼（沒有ui，只有初始腳本），但是在嘗試console.log時出現問題，用戶記錄了總花費，我的代碼僅使每筆購買的花費翻了一番項目，所以我決定在這里尋求幫助。

編碼：

//initial code

const account = {
    name: 'user',
    expenses: [],
    addExpense: function(description, amount) {
        account.expenses.push({
            description: description,
            amount: amount
        });
    },
    getAccountSummary: function() {
        let expenses = account.expenses;
        for (let i = 0; i < expenses.length; i++ ) {
            let value = expenses[i].amount + expenses[i].amount;
            console.log(value);
        }
    }
}

//output calls

account.addExpense('Milk', 8);
account.addExpense('Netflix', 30);
account.addExpense('Steam summer sale', 26);
account.addExpense('Coffee', 4);
console.log(account.getAccountSummary());

代碼始終在以下記錄此值：

16
60
52
8

實際上是輸入值（8、30、26、4）的兩倍。

我正在尋找的輸出是所有這些值的總和，在這種情況下：

68

希望我的問題清楚。

Answer 1

當您想要一個基於數組中項目的值時，您應該考慮reduce

const account = {
    name: 'user',
    expenses: [],
    addExpense: function(description, amount) {
        account.expenses.push({
            description: description,
            amount: amount
        });
    },
    getAccountSummary: function() {
       return account.expenses.reduce((acc,{amount}) => acc+amount,0);
    }
}

Answer 2

在您的getAccountSummary中

采用

let value = 0;
for (let i = 0; i < expenses.length; i++ ) {
     value += expenses[i].amount ;   
     console.log(value); 
}

希望對您有幫助。

Answer 3

expenses[i].amount加2倍，以expenses[i].amount let value = expenses[i].amount + expenses[i].amount; ，這就是為什么被加倍的原因。

如果要在getAccountSummary打印總和，則可以執行以下操作：

  getAccountSummary: function() {
      const expenses = account.expenses;
      let value = 0
      for (let i = 0; i < expenses.length; i++ ) {
          value += expenses[i].amount;
      }
      console.log(value);
  }

但是，如果您想在getAccountSummary上返回總和，以便可以打印它（這似乎更合理），則可以這樣做：

  getAccountSummary: function() {
      const expenses = account.expenses;
      let value = 0
      for (let i = 0; i < expenses.length; i++ ) {
          value += expenses[i].amount;
      }
      return value;
  }

並且您應該能夠調用console.log(account.getAccountSummary());

您也可以使用forEach（）迭代費用。

Answer 4

主要問題是您是直接記錄值，而不是返回它們以供以后記錄。

另外，在現代Javascript中也無需使用“ function”關鍵字。

這是我的解決方案，給出了預期的輸出。

const account = {

    name: 'user',
    expenses: [],

    addExpense(description, amount) {
        account.expenses.push({
            description: description,
            amount: amount
        });
    },

    getAccountSummary() {

        return account.expenses.reduce((result, expense) => result + expense.amount, 0)
    }
}

//output calls

account.addExpense('Milk', 8);
account.addExpense('Netflix', 30);
account.addExpense('Steam summer sale', 26);
account.addExpense('Coffee', 4);
console.log(account.getAccountSummary()); // 68