Redux combReducers does not pass state to the reducer

Question

In the following code, data is (state, action)not transmitted to the gears on combineReducers. It generates an error below. This is probably a small mistake that I am making. JSFiddle Link: https://jsfiddle.net/bengrunfeld/1h0t59uf/

import React from 'react'
import { render } from 'react-dom'
import { combineReducers } from 'redux'
import { Constants } from './constants/constants'


const goal = (state = 0, action) => {
  (action.type === Constants.ADD) ?
    state + action.payload:
    state
}

const target = (state = 0, action) => {
  (action.type === Constants.REMOVE)?
    state - action.payload:
    state
}

const reducer = combineReducers({
  goal,
  target
})

const state = 10

const newState = reducer(state, {
  type: Constants.REMOVE,
  payload: 5
})

render(
  <div>
    <p>{newState}</p>
  </div>,
  document.getElementById('main')
)

Error message

main.bundle.js:28054 Uncaught Error: Reducer "goal" returned undefined during initialization. If the state passed to the reducer is undefined, you must explicitly return the initial state. The initial state may not be undefined.
    at http://localhost:3000/main.bundle.js:28054:13
    at Array.forEach (native)
    at assertReducerSanity (http://localhost:3000/main.bundle.js:28049:25)
    at combineReducers (http://localhost:3000/main.bundle.js:28104:5)
    at Object.<anonymous> (http://localhost:3000/main.bundle.js:13236:42)
    at __webpack_require__ (http://localhost:3000/main.bundle.js:20:30)
    at Object.<anonymous> (http://localhost:3000/main.bundle.js:31673:18)
    at __webpack_require__ (http://localhost:3000/main.bundle.js:20:30)
    at module.exports (http://localhost:3000/main.bundle.js:66:18)
    at http://localhost:3000/main.bundle.js:69:10

Answer 1

const Constants = {
  REMOVE: "REMOVE",
  ADD: "ADD"
}

const goal = (state = 5, action) => {
  return (action.type === Constants.ADD) ?
    state + action.payload:
    state
}

const target = (state = 5, action) => {
  return (action.type === Constants.REMOVE)?
    state - action.payload:
    state
}

const reducer = Redux.combineReducers({
  goal,
  target
})

const state = {goal: 10, target:5}

const newState = reducer(state, {
  type: Constants.REMOVE,
  payload: 5
})

console.log(newState);

ReactDOM.render(
  <div>
    <p>{newState.goal}</p>
    <p>{newState.target}</p>
  </div>,
  document.getElementById('main')
)

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>

<script src="https://cdnjs.cloudflare.com/ajax/libs/redux/3.6.0/redux.min.js"></script>


<div id="main"></div>

Run codeHide result

• You need to determine the initial state for each of your gearboxes.
• You must also return the state from your gearbox.

Answer 2

You must tell Redux what will be the initial state.

Or in the gearboxes themselves (es6 default argument note)

: ,

const goal = (state = 0, action) => {
  return (action.type === Constants.ADD) ?
    state + action.payload:
    state
}

const target = (state = 0, action) => {
  return (action.type === Constants.REMOVE)?
    state - action.payload:
    state
}

CreateStore

: http://redux.js.org/docs/recipes/reducers/InitializingState.html