[React] How to use a setState Updater Function with a Reducer Pattern

In this lesson we'll walk through setting up an updater function that can receive an action argument. We'll also dive into how to separate your state management logic into a separate reducer function much like how Redux operates. It will receive an action which we can add any data and update state accordingly.

import React, { Component } from "react";

const INCREMENT = "INCREMENT";
const DECREMENT = "DECREMENT";

const reducer = action => (state, props) => {
  switch (action.type) {
    case INCREMENT:
      return {
        value: state.value + action.amount,
      };
    case DECREMENT:
      return {
        value: state.value - 1,
      };
    default:
      return null;
  }
};

class App extends Component {
  state = {
    value: 0,
  };
  increment = () => {
    this.setState(
      reducer({
        type: INCREMENT,
        amount: 2
      }),
    );
  };
  decrement = () => {
    this.setState(
      reducer({
        type: DECREMENT,
      }),
    );
  };
  render() {
    return (
      <div>
        <div>{this.state.value}</div>
        <button onClick={this.increment}>Increment</button>
        <button onClick={this.decrement}>Decrement</button>
      </div>
    );
  }
}

export default App;