Redux in 30 lines

redux.js

function createStore(reducer) {
    const store = {
        state: {},
        reducer,
        dispatch(action) {
            this.state = this.reducer(action, this.state)
        }
    }

    store.dispatch({})
    return store
}


function combineReducers(reducers) {
    return (action, state) => {
        const nextState = {}
        for (const key of Object.keys(reducers)) {
            nextState[key] = reducers[key](action, state[key])
        }

        return nextState
    }
}


module.exports = {
    createStore,
    combineReducers
}

test.js

const { createStore, combineReducers } = require('./redux.js')


function countReducer(action, count = 0) {
    switch(action.type) {
        case 'INC':
            count += 1
            break;
        default:
            break;
    }

    return count
}

function helloReducer(action, greeting = 'Hello, John!') {
    switch(action.type) {
        case 'NAME':
            greeting = `Hello, ${action.payload}!`
            break;
        default:
            break;
    }

    return greeting
}


const reducer = combineReducers({ count: countReducer, hello: helloReducer })
const store = createStore(reducer)

console.log(store.state)
store.dispatch({ type: 'INC' })
console.log(store.state)
store.dispatch({ type: 'INC' })
console.log(store.state)
store.dispatch({ type: 'NAME', payload: 'Sam' })
console.log(store.state)