React State (useState)

State is data that can change over time. The useState hook gives you a value and a function to update it. When you update state, React re-renders the component.

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

Press Run, then click the button in the result — the count updates without reloading. That is React keeping the screen in sync with the state.