Reactjs 在迭代状态时无法读取未定义的属性(读取 map )

我正试图通过Reaction创建一个非常简单的"待办事项 list ".我想要编辑一项任务，只要"编辑"按钮被点击，但之后出现上述错误.根据调试过程，我发现退出减速器作用域后，"任务"变得不确定.我想知道一个国家怎么可能变得不确定.以下是我的代码:

import { useReducer, useRef } from "react";

const App = () => {
  const idCreator = () => {
    return Math.floor(Math.random() * 100000);
  };

  const reducer = (state, action) => {
    switch (action.type) {
      case "add": {
        return [
          ...state,
          {
            task: action.task,
            isEditMode: false,
            isDeleteMode: false,
            id: idCreator()
          }
        ];
      }

      case "edit": {
        const tempObj = state.forEach((item) => {
          if (item.id === action.id) {
            return { ...item, isEditMode: !item.isEditMode };
          } else return item;
        });
        return tempObj;
      }

      default:
        return state;
    }
  };
  const [tasks, dispatch] = useReducer(reducer, []);

  const task = useRef("");

  return (
    <>
      <input
        placeholder="task..."
        onChange={(e) => {
          task.current = e.currentTarget.value;
        }}
      />
      <button
        onClick={() => {
          dispatch({ type: "add", task: task.current });
        }}
      >
        Add
      </button>
      <ul>
        {tasks.map((item) => {
          return (
            <li key={item.id}>
              <input
                value={item.task}
                style={{ display: item.isEditMode ? "inline-block" : "none" }}
                onChange={(e) => {
                  item.task = e.currentTarget.value;
                }}
              />
              <h3
                style={{ display: item.isEditMode ? "none" : "inline-block" }}
              >
                {item.task}
              </h3>
              <button
                style={{ display: "inline-block" }}
                onClick={() => {
                  dispatch({ type: "edit", id: item.id });
                }}
              >
                Edit
              </button>
              <button>Delete</button>
            </li>
          );
        })}
      </ul>
    </>
  );
};

export default App;

任何帮助都将不胜感激.