ReactJS：將新對象擴展到現有數組

Question

我有這個數組對象開始

[
  {
    "name": "child",
    "pax": {}
  }
]

我希望附加一個數組的新屬性。 那么我想將新對象更新/插入該數組。 但是我的代碼出了點問題

function App() {
  const [num, setNum] = useState(0);
  const [arr, setArr] = useState([
    {
      name: "child",
      pax: {}
    }
  ]);

  function appendage({ id, age }) {
    const toSaveArr = arr.map(o => {
      if (o.name === "child") {
        return {
          ...o,
          age: o.age
            ? o.age.map(o2 => {
                if (o2.id === id) {
                  return {
                    id: o2.id,
                    age
                  };
                }
                console.log("o2", o2);
                //something is wrong here
                //why is it not adding new object?
                return [
                  ...o2,
                  {
                    id,
                    age
                  }
                ];
              })
            : [{ id, age }]
        };
      }
      return o;
    });

    setArr(toSaveArr);
  }

  return (
    <div className="App">
      <h1>{num}</h1>
      <button
        onClick={() => {
          setNum(num + 1);

          appendage({
            id: num + 1,
            age: num + 1
          });
        }}
      >
        add
      </button>
      <button>update age where id equal to 2</button>
      <pre>{JSON.stringify(arr, null, 2)}</pre>
    </div>
  );
}

https://codesandbox.io/s/pedantic-mclean-107q2

我想我在這里錯誤地使用了傳播算子。

Answer 1

問題是傳遞給map的函數返回一個數組，但這不是map工作方式。 您只能更改數組中的現有對象，而不能添加新對象。 您可以使用例如find數組中的對象並檢查結果是否undefined 。

const result = o.age.find(o2 => o2.id === id);
if (result) {
    result.age = age;
} else {
    o.age.push({ id: o2.id, age: age });
}

Answer 2

您可以在數組中使用find方法來查找特定值，在此處是"child" ：

import React, { useState, useDebugValue } from "react";
import styled from "styled-components";
import ReactDOM from "react-dom";

import "./styles.css";

function App() {
  const [num, setNum] = useState(0);
  const [arr, setArr] = useState([
    {
      name: "child",
      pax: []
    }
  ]);

  function appendage({ id, age }) {
    var newarr = arr;
    var add = {
      id: id,
      age: age
    };
    newarr.find(el => el.name === "child").pax = [
      ...newarr.find(el => el.name === "child").pax,
      add
    ];

    setArr(newarr);
  }

  return (
    <div className="App">
      <h1>{num}</h1>
      <button
        onClick={() => {
          setNum(num + 1);

          appendage({
            id: num + 1,
            age: num + 1
          });
        }}
      >
        add
      </button>
      <button>update age where id equal to 2</button>
      <pre>{JSON.stringify(arr, null, 2)}</pre>
    </div>
  );
}

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

Answer 3

我們檢查是否已經存在年齡對象，如果是，則使用傳播運算符添加一個新對象； 如果沒有，我們插入對象；

相關代碼 ：

import React, { useState } from "react";
import styled from "styled-components";
import ReactDOM from "react-dom";

import "./styles.css";

function App() {
  const [num, setNum] = useState(0);
  const [arr, setArr] = useState([
    {
      name: "child",
      pax: {}
    }
  ]);

  function appendage({ id, age }) {
    console.log("inside appendage with ", id, " and age:", age);
    const toSaveArr = arr.map(o => {
      if (o.name === "child") {
        if (o.age) {
          console.log("age exists");
          o.age = [
            ...o.age,
            {
              id: id,
              age: age
            }
          ];
          console.log("O", o);
        } else {
          o.age = [
            {
              id: id,
              age: age
            }
          ];
          console.log("O", o);
        }
        /*return {
          ...o,
          age: o.age
            ? o.age.map(o2 => {
                if (o2.id === id) {
                  return {
                    id: o2.id,
                    age
                  };
                }
                console.log("o2", o2);
                //something is wrong here
                //why is it not adding new object?
                return [
                  ...o2,
                  {
                    id,
                    age
                  }
                ];
              })
            : [{ id, age }]
        };
      */
      }
      return o;
    });

    setArr(toSaveArr);
  }

  return (
    <div className="App">
      <h1>{num}</h1>
      <button
        onClick={() => {
          setNum(num + 1);

          appendage({
            id: num + 1,
            age: num + 1
          });
        }}
      >
        add
      </button>
      <button>update age where id equal to 2</button>
      <pre>{JSON.stringify(arr, null, 2)}</pre>
    </div>
  );
}

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

這里的工作代碼和盒子