错误：Reducer“计数器”在初始化期间返回未定义。如果传递给reducer的状态是未定义的

Question

我正在尝试对 reduxer（学习）进行基本测试，看起来基本没有问题，但我收到此错误“\xc3\x97\n错误：Reducer“计数器”在初始化期间返回未定义。如果状态传递给“reducer 未定义，必须显式返回初始状态。初始状态不一定是未定义的。如果你不想给这个reducer 设置值，可以使用 null 代替 undefined。”

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我相信这个反应是非常愚蠢的希望得到帮助。

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Reduxer 文件。\ncounter.js

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const counterReducer = (state = 0, action) => {\n  switch (action.type) {\n    case "INCREMENT":\n      return state + 1;\n    case "DECREMENT":\n      return state - 1;\n  }\n};\n\nexport default counterReducer;

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isLogged.js

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const loggedReducer = (state = false, action) => {\n  switch (action.type) {\n    case "SING_IN":\n      return !state;\n    default:\n      return state;\n  }\n};\nexport default loggedReducer;

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\r\n\nindex.js

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import counterReducer from "./counter";\nimport loggedReducer from "./isLogged";\nimport { combineReducers } from "redux";\n\nconst allReducers = combineReducers({\n  counter: counterReducer,\n  isLogged: loggedReducer,\n});\n\nexport default allReducers;

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src 文件夹>index.js。

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import React from "react";\nimport ReactDOM from "react-dom";\nimport "./index.css";\nimport App from "./App";\nimport * as serviceWorker from "./serviceWorker";\nimport { createStore } from "redux";\nimport allReducer from "./reducers";\n\nconst store = createStore(\n  allReducer,\n  window.__REDUX_DEVTOOLS_EXTENSION__ && window.__REDUX_DEVTOOLS_EXTENSION__()\n);\n\nReactDOM.render(\n  <React.StrictMode>\n    <App />\n  </React.StrictMode>,\n  document.getElementById("root")\n);\n\n\nserviceWorker.unregister();

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Answer 1

你应该默认从reducer返回

const counterReducer = (state = 0, action) => {
  switch (action.type) {
    case "INCREMENT":
      return state + 1;
    case "DECREMENT":
      return state - 1;
    default:
      return state;
  }
};

每个减速器都会收到发送的每个操作。如果您不知道操作类型，则应该原封不动地返回状态。