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useState Hook

React.js docs for useState

The setState function is used to update the state. It accepts a new state value and enqueues a re-render of the component.

A Simple Counter Example

type action =
  | Tick;

type state = {count: int};

[@react.component]
let make = (~initialCount) => {
  let (count, setCount) = React.useState(_ => initialCount);

  <>
    {React.string("Count: " ++ string_of_int(count))}
    <button onClick={_ => setCount(_ => initialCount)}>
      {React.string("Reset")}
    </button>
    <button onClick={_ => setCount(prevCount => prevCount - 1)}>
      {React.string("-")}
    </button>
    <button onClick={_ => setCount(prevCount => prevCount + 1)}>
      {React.string("+")}
    </button>
  </>;
};