FocusThen

import React from 'react';
import ReactDOM from 'react-dom';

let callCount = -1
let states = []

function useState(initValue) {
  const id = ++callCount
  
  if (states[id]) return states[id]

FocusThen

<div id="app"></div>
<script>
    // Create virtual node
    function h(tag, props, children) {
        // Return the virtual node
        return {
            tag,
            props,
            children,
        }

FocusThen

<script>
    let activeEffect

    class Dep {
        // Initialize the value of the reactive dependency
        constructor(value) {
            this._value = value
            this.subscribers = new Set()
        }

FocusThen

<script>
    let activeEffect

    class Dep {
        subscribers = new Set()
        depend() {
            if (activeEffect) this.subscribers.add(activeEffect)
        }
        notify() {
            this.subscribers.forEach((sub) => sub())

FocusThen

<style>
    * {
        user-select: none;
    }
    body {
        margin: 0;
        font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
    }
    #app {
        height: 100vh;