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HTML Settings

Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

      <span id="a"></span>
      <span id="b"></span>
      <span id="c"></span>

    <input type="button" onclick="store.a++" value="a++" />
    <input type="button" onclick="store.a--" value="a--" />

    <input type="button" onclick="store.b++" value="b++" />
    <input type="button" onclick="store.b--" value="b--" />

              * {
  text-align: center;
  font-size: 1.9rem;

#a, #b, #c {
  transition: background-color 500ms linear;

.highlight {
  background-color: lightgreen;

              const $ = document.getElementById.bind(document);

// View Model / Data Store
const store = {
  a: 2,
  b: 4

window.store = store;

function highlight(id) {
  setTimeout(() => $(id).classList.remove('highlight'), 1000);

// Render functions
function renderA() {
  $('a').innerHTML = store.a * store.a;

function renderB() {
  $('b').innerHTML = store.b * store.b;

function renderC() {
  $('c').innerHTML = (store.a * store.a) + (store.b * store.b);

// Start reactivity logic
let currentFn = null;

window.Dep = class {
  constructor() {
    this.deps = new Set();

  depend() {
    if (currentFn) {

  notify() {
    this.deps.forEach(fn => fn());

function makeObjectReactive(obj) {
  Object.keys(obj).forEach(k => {
    let value = obj[k];
    let dep = new Dep();
    Object.defineProperty(obj, k, {
      get() {
        console.log(`Getting property ${k}`);
        return value;
      set(val) {
        console.log(`Setting property ${k} = ${val}`);
        value = val;
  return obj;

function makeFunctionReactiveAndExecute(fn) {
  function wrapped() {
    currentFn = fn;
    currentFn = null;

// Make our store object reactive with dependencies 
// against currentFn

// Make all of our functions reactive so theyre tracked 
// in currentFn and perform our initial render
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