reducer.js

/*
Lien utile : https://www.youtube.com/watch?v=TOhUqDGNFtA
*/

const ACTIONS = {
  INCREMENT: "increment",
  DECREMENT: "decrement",
  RESET: "reset",
};

/**
 * @param { Object } state : l'état courrant
 * @param {{type : string, payload : *}} action : action à appliquer. Contient un type et un contenu (payload)
 * @returns { Object } le nouveau état modifié (ou non) par l'action
 */
const reducer = (state, action) => {
  switch (action.type) {
    case ACTIONS.INCREMENT:
      return { name: state.name, count: state.count + action.payload };
    case ACTIONS.DECREMENT:
      return { name: state.name, count: state.count - action.payload };
    case ACTIONS.RESET:
      return { name: state.name, count: 0 };
    default:
      return state;
  }
};

let counter = { name: "Timer", count: 0 };
const incrementAction = { type: ACTIONS.INCREMENT, payload: 1 };

counter = reducer(counter, incrementAction);
console.log(counter); // { name: 'Timer', count: 1}

counter = reducer(counter, { type: ACTIONS.INCREMENT, payload: 10 });
console.log(counter); // { name: 'Timer', count: 11}

counter = reducer(counter, { type: ACTIONS.DECREMENT, payload: 5 });
console.log(counter); // { name: 'Timer', count: 6}

counter = reducer(counter, { type: ACTIONS.RESET });
console.log(counter); // { name: 'Timer', count: 0}