Simple example of state, actions, and reducers

kinda-redux.js

const INCREMENT = Symbol('INCREMENT');
const DECREMENT = Symbol('DECREMENT');

const makeReducer = (initialState, reducers = {}, props = {}) =>
    (state = initialState, action) =>
        reducers.hasOwnProperty(action.type) ? reducers[action.type](state, action) : state;

const reducer = makeReducer(42, {
    [INCREMENT]: (state, action) => state + 1,
    [DECREMENT]: (state, action) => state - 1
});

const makeAction = (type) => ({ type });

const run = (reducer) => (actions) => actions.reduce((state, action) => {
    const next = reducer(state, action);
    console.log({
        previous: state,
        action: action.type.toString(),
        next
    });
    return next;
}, reducer(undefined, {}));

run(reducer)([
    INCREMENT, INCREMENT, INCREMENT, DECREMENT, INCREMENT
].map(makeAction));