2.5 KiB

Raw Blame History

id	title	challengeType	forumTopicId	dashedName
5a24c314108439a4d403615a	Remove an Item from an Array	6	301447	remove-an-item-from-an-array

--description--

Time to practice removing items from an array. The spread operator can be used here as well. Other useful JavaScript methods include slice() and concat().

--instructions--

The reducer and action creator were modified to remove an item from an array based on the index of the item. Finish writing the reducer so a new state array is returned with the item at the specific index removed.

--hints--

The Redux store should exist and initialize with a state equal to [0,1,2,3,4,5]

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

removeItem and immutableReducer both should be functions.

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

Dispatching the removeItem action creator should remove items from the state and should NOT mutate 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);

2.5 KiB Raw Blame History