freeCodeCamp/curriculum/challenges/english/03-front-end-libraries/redux/copy-an-object-with-object.assign.english.md

id	title	challengeType	isRequired
5a24c314108439a4d403615b	Copy an Object with Object.assign	6	false

Description

The last several challenges worked with arrays, but there are ways to help enforce state immutability when state is an object, too. A useful tool for handling objects is the Object.assign() utility. Object.assign() takes a target object and source objects and maps properties from the source objects to the target object. Any matching properties are overwritten by properties in the source objects. This behavior is commonly used to make shallow copies of objects by passing an empty object as the first argument followed by the object(s) you want to copy. Here's an example: const newObject = Object.assign({}, obj1, obj2); This creates newObject as a new object, which contains the properties that currently exist in obj1 and obj2.

Instructions

The Redux state and actions were modified to handle an object for the state. Edit the code to return a new state object for actions with type ONLINE, which set the status property to the string online. Try to use Object.assign() to complete the challenge.

Tests

tests:
  - text: The Redux store should exist and initialize with a state that is equivalent to the <code>defaultState</code> object declared on line 1.
    testString: 'assert((function() { const expectedState = { user: ''CamperBot'', status: ''offline'', friends: ''732,982'', community: ''freeCodeCamp'' }; const initialState = store.getState(); return DeepEqual(expectedState, initialState); })(), ''The Redux store should exist and initialize with a state that is equivalent to the <code>defaultState</code> object declared on line 1.'');'
  - text: <code>wakeUp</code> and <code>immutableReducer</code> both should be functions.
    testString: assert(typeof wakeUp === 'function' && typeof immutableReducer === 'function', '<code>wakeUp</code> and <code>immutableReducer</code> both should be functions.');
  - text: Dispatching an action of type <code>ONLINE</code> should update the property <code>status</code> in state to <code>online</code> and should NOT mutate state.
    testString: 'assert((function() { const initialState = store.getState(); const isFrozen = DeepFreeze(initialState); store.dispatch({type: ''ONLINE''}); const finalState = store.getState(); const expectedState = { user: ''CamperBot'', status: ''online'', friends: ''732,982'', community: ''freeCodeCamp'' }; return isFrozen && DeepEqual(finalState, expectedState); })(), ''Dispatching an action of type <code>ONLINE</code> should update the property <code>status</code> in state to <code>online</code> and should NOT mutate state.'');'
  - text: <code>Object.assign</code> should be used to return new state.
    testString: getUserInput => assert(getUserInput('index').includes('Object.assign'), '<code>Object.assign</code> should be used to return new state.');

Challenge Seed

const defaultState = {
  user: 'CamperBot',
  status: 'offline',
  friends: '732,982',
  community: 'freeCodeCamp'
};

const immutableReducer = (state = defaultState, action) => {
  switch(action.type) {
    case 'ONLINE':
      // don't mutate state here or the tests will fail
      return
    default:
      return state;
  }
};

const wakeUp = () => {
  return {
    type: 'ONLINE'
  }
};

const store = Redux.createStore(immutableReducer);

Solution

const defaultState = {
  user: 'CamperBot',
  status: 'offline',
  friends: '732,982',
  community: 'freeCodeCamp'
};

const immutableReducer = (state = defaultState, action) => {
  switch(action.type) {
    case 'ONLINE':
      return Object.assign({}, state, {
        status: 'online'
      });
    default:
      return state;
  }
};

const wakeUp = () => {
  return {
    type: 'ONLINE'
  }
};

const store = Redux.createStore(immutableReducer);