lmuntaner/app-use-state.js

## app-use-state.js
const createElement = (tag, props, children ) => ({ tag, props, children });

const hooks = [];
let useStateCalls = -1;

const useState = (initialState) => {
  useStateCalls += 1;
  // Each hook is an array with two elements:
  // - hook[0] is the state
  // - hook[1] is the setState function
  if (hooks[useStateCalls] === undefined) {
    const hook = [initialState]
    hooks[useStateCalls] = hook;
    hook[1] = (updatedState) => {
      console.log('in da setState');
      hook[0] = updatedState;
      renderApp();
    }
  }
  return hooks[useStateCalls];
}


const render = (vnode, parent) => {
  if (typeof vnode === "string" || typeof vnode === "number") {
    return parent.appendChild(document.createTextNode(vnode));
  }

  if (typeof vnode.tag === "function") {
    const nextVNode = vnode.tag(vnode.props);
    return render(nextVNode, parent);
  }

  const element = document.createElement(vnode.tag);

  if (vnode.props) {
    Object.keys(vnode.props).forEach(key => {
      const value = vnode.props[key];
      // Add event listeners from props `on<Event>`
      if (key.startsWith("on")) {
        const event = key.slice(2).toLowerCase();
        element.addEventListener(event, value);
      } else {
        element.setAttribute(key, value);
      }
    });
  }

  if (vnode.children) {
    vnode.children.forEach(child => render(child, element));
  }
  return parent.appendChild(element);
};

const Title = () => createElement("h1", {}, ["Hello from dynamic app!"]);

const Counter = () => {
  const [count, setCount] = useState(0);
  const increment = () => {
    setCount(count + 1);
  };
  const decrement = () => {
    setCount(count - 1);
  };
  return createElement("div", {}, [
    createElement("button", { onClick: increment }, ["+"]),
    createElement("h3", {}, [count]),
    createElement("button", { onClick: decrement }, ["-"]),
  ])
}

const createApp2 = () => createElement(
  "div",
  {},
  [
    createElement(Title, {}, []),
    createElement(Counter, {}, []),
    createElement("p", {}, ["This was build with `createElement`"])
  ]
);

const renderApp = () => {
  useStateCalls = -1;
  const parent = document.getElementById("root");
  parent.innerHTML = "";
  render(createApp2(), parent);
};

renderApp();

## index.html
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div id="root"></div>

  <script src="./app-use-state.js"></script> -->
</body>
</html>
	const createElement = (tag, props, children ) => ({ tag, props, children });

	const hooks = [];
	let useStateCalls = -1;

	const useState = (initialState) => {
	useStateCalls += 1;
	// Each hook is an array with two elements:
	// - hook[0] is the state
	// - hook[1] is the setState function
	if (hooks[useStateCalls] === undefined) {
	const hook = [initialState]
	hooks[useStateCalls] = hook;
	hook[1] = (updatedState) => {
	console.log('in da setState');
	hook[0] = updatedState;
	renderApp();
	}
	}
	return hooks[useStateCalls];
	}


	const render = (vnode, parent) => {
	if (typeof vnode === "string" \|\| typeof vnode === "number") {
	return parent.appendChild(document.createTextNode(vnode));
	}

	if (typeof vnode.tag === "function") {
	const nextVNode = vnode.tag(vnode.props);
	return render(nextVNode, parent);
	}

	const element = document.createElement(vnode.tag);

	if (vnode.props) {
	Object.keys(vnode.props).forEach(key => {
	const value = vnode.props[key];
	// Add event listeners from props `on<Event>`
	if (key.startsWith("on")) {
	const event = key.slice(2).toLowerCase();
	element.addEventListener(event, value);
	} else {
	element.setAttribute(key, value);
	}
	});
	}

	if (vnode.children) {
	vnode.children.forEach(child => render(child, element));
	}
	return parent.appendChild(element);
	};

	const Title = () => createElement("h1", {}, ["Hello from dynamic app!"]);

	const Counter = () => {
	const [count, setCount] = useState(0);
	const increment = () => {
	setCount(count + 1);
	};
	const decrement = () => {
	setCount(count - 1);
	};
	return createElement("div", {}, [
	createElement("button", { onClick: increment }, ["+"]),
	createElement("h3", {}, [count]),
	createElement("button", { onClick: decrement }, ["-"]),
	])
	}

	const createApp2 = () => createElement(
	"div",
	{},
	[
	createElement(Title, {}, []),
	createElement(Counter, {}, []),
	createElement("p", {}, ["This was build with `createElement`"])
	]
	);

	const renderApp = () => {
	useStateCalls = -1;
	const parent = document.getElementById("root");
	parent.innerHTML = "";
	render(createApp2(), parent);
	};

	renderApp();
	<!DOCTYPE html>
	<html lang="en">
	<head>
	<meta charset="UTF-8">
	<meta http-equiv="X-UA-Compatible" content="IE=edge">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>Document</title>
	</head>
	<body>
	<div id="root"></div>

	<script src="./app-use-state.js"></script> -->
	</body>
	</html>