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// Action
const COUNT_UP = "COUNT_UP";
function countUp() {
return {
type: COUNT_UP
// Reducer
function reducer(state, action) {
switch (action.type) {
case COUNT_UP:
return state + 1;
return state
// State Store
let store = 0; // Initial state
document.addEventListener('action', function(e) {
store = reducer(store, e.detail);
document.dispatchEvent(new CustomEvent('state'));
}, false);
// UI state change method
function render() {
let $div = document.querySelector('div');
$div.innerHTML = store;
document.addEventListener('state', render);
// UI event handler
let $button = document.querySelector('button');
$button.addEventListener("click", function() {
new CustomEvent('action', { detail: countUp()})