运算符“+”不能应用于类型“{}”和 'number'

Question

我正在尝试根据来自后端的查询计算我的应用程序中的银行余额，结果如下：

{
    "previousBalance": 60,
    "data": [
        {
            "id": "6fbc24fa-7262-4c82-8944-134201ca2524",
            "bank_statement_id": "3d3a6fdc-66e3-412e-9c3a-493681a0504e",
            "date": "2021-02-24T03:00:00.000Z",
            "value": 333.33
        },
        {
            "id": "98e1c331-a2cc-4e6c-b466-6e778bb1ad10",
            "bank_statement_id": "d62c2bbb-fcf1-4227-9bdb-e7f7ba00099d",
            "date": "2021-02-24T03:00:00.000Z",
            "value": -200
        },
        {
            "id": "1ede9e5c-3b29-450a-bfa3-655ab62ed489",
            "bank_statement_id": "d62c2bbb-fcf1-4227-9bdb-e7f7ba00099d",
            "date": "2021-02-24T03:00:00.000Z",
            "value": -68.33
        }
    ]
}

以此为目的，在每笔交易中留下每笔交易的余额值，逻辑如下

type Transaction = {
    id: string,
    bank_statement_id: string,
    date: string,
    value: number,
    created_at: string,
    updated_at: string,
}

const transactions: Transaction[] = [...];

const transactionsFormated = transactions.map((transaction:, index) => {
        const totalBalance = transactions.reduce((acc: number, transaction, currentIndex) => {
            if(currentIndex <= index) {
                return acc + transaction.value;
            }
            return acc;
        });
        return {
            ...transaction,
            balance: previousBalance + totalBalance, 
        }
    });

然而，VSCode 指出 acc 参数是交易类型，而不是数字类型，此外还有标题中的消息post.

我该如何处理这个问题？

Answer 1

您缺少reduce方法的第二个参数，即初始值；如果没有，初始值是数组的第一个元素，这是一个事务。

...
        const totalBalance = transactions.reduce((acc: number, transaction, currentIndex) => {
            if(currentIndex <= index) {
                return acc + transaction.value;
            }
            return acc;
        }, 0); // <=== here add the initial value
...

运算符“+”不能应用于类型“{}”和 'number'

Operator '+' cannot be applied to types '{}' and 'number'

reduce

typescript