Redux - 每次使用新变量在reducer switch语句中定义新状态？

Question

我的减速器是这样的：

switch (action.type) {
      case "UPDATE_CURRENT_USER":
        let newState = {...state, ...action.payload };
        return newState;
      case "GET_CURRENT_USER":
        return state;
      case "UPDATE_USERNAME":
        newState = {...state, name: action.payload.name};
        return state;
  }

现在，我第二次使用newState 我不再定义它了。我只是使用上面定义的变量。这个可以吗？ 我想重新定义它，但出错了。但我不确定这种方式是否仍然会给我正确的结果 - 尽管一切似乎都工作正常？

Answer 1

您无需为新状态创建变量，为其赋值并返回它。相反，您可以立即返回新的状态值。并且不要忘记在最后添加一个默认情况。

switch (action.type) {
        case 'UPDATE_CURRENT_USER':
          return { ...state, ...action.payload };
        case 'GET_CURRENT_USER':
          return state;
        case 'UPDATE_USERNAME':
          return { ...state, name: action.payload.name };
        default:
          return state;
      }

Answer 2

使用花括号 {} 在 case 语句内创建新的块作用域：

switch (action.type) {
  case "UPDATE_CURRENT_USER": {
    let newState = {...state, ...action.payload };
    return newState;
  }
  case "GET_CURRENT_USER":
    return state;
  case "UPDATE_USERNAME": {
    let newState = {...state, name: action.payload.name};
    return newState;
  }
}

由于let 和const 是块范围的局部变量，它们仅在当前块中可见。

我你的代码你正在使用未声明的newState 变量：

switch (action.type) {
  case "UPDATE_CURRENT_USER":
    // (conditionaly) declaring block scoped variable newState
    let newState = {...state, ...action.payload };
    return newState;
  case "UPDATE_USERNAME":
    // here you cannot declare newState variable because it might be declared before
    // however the variable is not declared since we are in other case
    // so that here you are using global window variable window.newState
    newState = {...state, name: action.payload.name};
    return state;
}