Use the Spread Operator on Arrays

Tell us what’s happening:

Your code so far

const immutableReducer = (state = ['Do not mutate state!'], action) => {
  switch(action.type) {
    case 'ADD_TO_DO':
      // don't mutate state here or the tests will fail
      return state;

const addToDo = (todo) => {
  return {
    type: 'ADD_TO_DO',

const store = Redux.createStore(immutableReducer);

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Link to the challenge:

What have you tried so far? The code you’ve provided seems to be exactly what you’re starting with in the course.

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