I'm trying to calculate the bank balance in my application from a query from my backend that has the following result:

{
    "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
        }
    ]
}

With that, it aimed to leave in each transaction, the balance value of each transaction with the following logic

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, 
        }
    });

However, the VSCode points out that the acc parameter is of type Transaction, instead of type number, in addition to the message as in the title of this post.

How can I proceed with this problem in question?

CodePudding user response：

You are missing the second parameter of the reduce method, which is the initial value; without that, the initial value is the first element of the array, which is a transaction.

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