React

the intro

React is a JavaScript library for building user interfaces out of small, reusable pieces called components. You describe what the screen should look like for a given state, and React figures out how to update the page when that state changes. Once it clicks, you stop fighting the DOM forever.

the sample

a real component, in full

function Counter() {
  const [n, setN] = useState(0)
  return (
    <button onClick={() => setN(n + 1)}>
      Clicked {n} times
    </button>
  )
}

the docs