14.14 Updating State Immutably

Counter.js

Counter.js

import React, { Component } from "react";
import { connect } from "react-redux";
import CounterControl from "../../components/CounterControl/CounterControl";
import CounterOutput from "../../components/CounterOutput/CounterOutput";

class Counter extends Component {
  render() {
    return (
      <div>
        <CounterOutput value={this.props.ctr} />
        <CounterControl
          label="Increment"
          clicked={this.props.onIncrementCounter}
        />
        <CounterControl
          label="Decrement"
          clicked={this.props.onDecrementCounter}
        />
        <CounterControl label="Add 5" clicked={this.props.onAddCounter} />
        <CounterControl
          label="Subtract 5"
          clicked={this.props.onSubtractCounter}
        />
        <hr />
        <button onClick={this.props.onStoreResult}>Store Result</button>
        <ul>
          {this.props.storedResults.map((strResult) => (
            <li key={strResult.id} onClick={this.props.onDeleteResult}>
              {strResult.value}
            </li>
          ))}
        </ul>
      </div>
    );
  }
}

const mapStateToProps = (state) => {
  return {
    ctr: state.counter,
    storedResults: state.results,
  };
};

const mapDispatchToProps = (dispatch) => {
  return {
    onIncrementCounter: () => dispatch({ type: "INCREMENT" }),
    onDecrementCounter: () => dispatch({ type: "DECREMENT" }),
    onAddCounter: () => dispatch({ type: "ADD", value: 5 }),
    onSubtractCounter: () => dispatch({ type: "SUBTRACT", value: 5 }),
    onStoreResult: () => dispatch({ type: "STORE_RESULT" }),
    onDeleteResult: () => dispatch({ type: "DELETE_RESULT" }),
  };
};
export default connect(mapStateToProps, mapDispatchToProps)(Counter);

reducer.js

reducer.js

const initialState = {
  counter: 0,
  results: [],
};

const reducer = (state = initialState, action) => {
  switch (action.type) {
    case "INCREMENT":
      const newState = Object.assign({}, state);
      newState.counter = state.counter + 1;
      return newState;
    case "DECREMENT":
      return {
        ...state,
        counter: state.counter - 1,
      };

    case "ADD":
      return {
        ...state,
        counter: state.counter + action.value,
      };

    case "SUBTRACT":
      return {
        ...state,
        counter: state.counter - action.value,
      };
    case "STORE_RESULT":
      return {
        ...state,
        results: state.results.concat({ id: new Date(), value: state.counter }),
      };
    default:
  }
  return state;
};

export default reducer;