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id	title	challengeType	forumTopicId	dashedName
5a24c314108439a4d403615a	從數組中刪除項目	6	301447	remove-an-item-from-an-array

--description--

是時候練習從數組中刪除項目了。擴展運算符也可以在這裏使用。其他有用的JavaScript方法包括 slice() 和 concat()。

--instructions--

reducer 和 action creator 被修改爲根據項目的索引從數組中刪除一個項目。完成編寫 reducer 以便返回一個新的狀態數組，並刪除特定索引處的項目。

--hints--

Redux store 應該存在並初始化一個 [0,1,2,3,4,5] 的狀態。

assert(
  (function () {
    const initialState = store.getState();
    return (
      Array.isArray(initialState) === true &&
      DeepEqual(initialState, [0, 1, 2, 3, 4, 5])
    );
  })()
);

removeItem 和 immutableReducer 都應該是一個函數。

assert(
  typeof removeItem === 'function' && typeof immutableReducer === 'function'
);

dispatch removeItem action creator 應該從 state 中刪除項目，不應該改變 state。

assert(
  (function () {
    const initialState = store.getState();
    const isFrozen = DeepFreeze(initialState);
    store.dispatch(removeItem(3));
    const state_1 = store.getState();
    store.dispatch(removeItem(2));
    const state_2 = store.getState();
    store.dispatch(removeItem(0));
    store.dispatch(removeItem(0));
    store.dispatch(removeItem(0));
    const state_3 = store.getState();
    return (
      isFrozen &&
      DeepEqual(state_1, [0, 1, 2, 4, 5]) &&
      DeepEqual(state_2, [0, 1, 4, 5]) &&
      DeepEqual(state_3, [5])
    );
  })()
);

--seed--

--seed-contents--

const immutableReducer = (state = [0,1,2,3,4,5], action) => {
  switch(action.type) {
    case 'REMOVE_ITEM':
      // Don't mutate state here or the tests will fail
      return
    default:
      return state;
  }
};

const removeItem = (index) => {
  return {
    type: 'REMOVE_ITEM',
    index
  }
}

const store = Redux.createStore(immutableReducer);

--solutions--

const immutableReducer = (state = [0,1,2,3,4,5], action) => {
  switch(action.type) {
    case 'REMOVE_ITEM':
      return [
        ...state.slice(0, action.index),
        ...state.slice(action.index + 1)
      ];
    default:
      return state;
  }
};

const removeItem = (index) => {
  return {
    type: 'REMOVE_ITEM',
    index
  }
}

const store = Redux.createStore(immutableReducer);

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