react-lea-1

import React from "react";
import "./style.css";

export default function App() {
  const [cnt, setCnt] = React.useState(function() {
    return Math.floor(Math.random(1) * 10);
  });
  const [k, setK] = React.useState(() => 20);
  React.useEffect(
    function() {
      console.log("rendered");
    },
    [k]//optional
  );
  function increment() {
    setCnt(function(prevCnt) {
      return prevCnt + 1;
    });
  }
  function decrement() {
    setCnt(function(prevCnt) {
      return prevCnt - 1;
    });
  }
  function modK() {
    setK(pk => pk + 1);
  }

  return (
    <React.Fragment>
      <button onClick={decrement}>-</button>
      <b>{cnt}</b>
      <button onClick={increment}>+</button>
      <br />
      <b>{k}</b>
      <button onClick={modK}>mod k</button>
    </React.Fragment>
  );
}