陣列concat正在覆寫for..each回圈中的值-有解無憂

const states = ["BR", "UP"];
const template = [
    {
      "State": "",
      "allotment": 25622
    },
    {
      "State": "",
      "expenditure": 1254
    }
  ];

let totalRecords: any[] = [];
states.forEach(state=>{
  const cc = template.map(record=> {record.State = state; return record})
  console.log(state, cc);// here i get the indiviual record set.
  totalRecords = totalRecords.concat(cc);
})
console.log(totalRecords);

在這里，我試圖獲得具有不同狀態的模板的串聯串列，但不知何故它覆寫了以前的記錄。盡管在將地圖添加到模板后在控制臺中可以看到，但可以看到正確的記錄集。仍然沒有正確連接。

如何正確執行所需的結果是

[{
  "State": "BR",
  "allotment": 25622
}, {
  "State": "BR",
  "expenditure": 1254
}, {
  "State": "UP",
  "allotment": 25622
}, {
  "State": "UP",
  "expenditure": 1254
}]

uj5u.com熱心網友回復：

問題是您正在重用來自的物件template，只是覆寫了這些物件的屬性。如果您想為每個狀態創建多個物件，則需要創建新物件：

const cc = template.map((record) => {
    record = { ...record, State: state }; // ***
    return record;
});

現場示例：

顯示代碼片段

const states = ["BR", "UP"];
const template = [
    {
        State: "",
        allotment: 25622,
    },
    {
        State: "",
        expenditure: 1254,
    },
];

let totalRecords /*: any[]*/ = [];
states.forEach((state) => {
    const cc = template.map((record) => {
        record = { ...record, State: state };
        return record;
    });
    console.log(state, cc);
    totalRecords = totalRecords.concat(cc);
});
console.log(totalRecords);

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

uj5u.com熱心網友回復：

你可以像這樣使用flatMap和map

const states = ["BR", "UP"];
const template = [
    {
      "State": "",
      "allotment": 25622
    },
    {
      "State": "",
      "expenditure": 1254
    }
  ];


const totalRecords =  states.flatMap(State=> template.map(record=> ({...record, State})))

console.log(totalRecords)

uj5u.com熱心網友回復：

您的程式中的問題出在此處： template.map(record=> {record.State = state; return record})

您沒有回傳一個新物件，而是覆寫了前一個物件，并且物件參考存盤在陣列中。它們都指向同一個，在記憶體中。

嘗試這個：

const states = ["BR", "UP"];
const template = [
    {
      "State": "",
      "allotment": 25622
    },
    {
      "State": "",
      "expenditure": 1254
    }
  ];

let totalRecords: any[] = [];
states.forEach(state=>{
  const cc = template.map(record=> ({...record, 'State': state}))
  totalRecords = totalRecords.concat(cc);
})
console.log(totalRecords);

這篇文章應該有所幫助。

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標籤：javascript 节点.js 数组级联

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