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id	title	challengeType	isRequired	forumTopicId
5a24c314108439a4d403615a	Remove an Item from an Array	6	false	301447

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.

Tests

tests:
  - text: The Redux store should exist and initialize with a state equal to <code>[0,1,2,3,4,5]</code>
    testString: assert((function() { const initialState = store.getState(); return (Array.isArray(initialState) === true && DeepEqual(initialState, [0, 1, 2, 3, 4, 5])); })());
  - text: <code>removeItem</code> and <code>immutableReducer</code> both should be functions.
    testString: assert(typeof removeItem === 'function' && typeof immutableReducer === 'function');
  - text: Dispatching the <code>removeItem</code> action creator should remove items from the state and should NOT mutate state.
    testString: 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]); })());

Challenge Seed

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);

Solution

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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