import React, { useState } from "react";import {BrowserRouter as Router, Switch, Route, Link, Prompt} from "react-router-dom";export default function PreventingTransitionsExample() {
  return (
    <Router>
      <ul><li><Link to="/">Form</Link></li>
             <li><Link to="/one">One</Link></li>
             <li><Link to="/two">Two</Link></li>
      </ul>
      <Switch>
        <Route path="/" exact children={<BlockingForm />} />
        <Route path="/one" children={<h3>One</h3>} />
        <Route path="/two" children={<h3>Two</h3>} />
      </Switch>
    </Router>
  );}function BlockingForm() {
  let [isBlocking, setIsBlocking] = useState(false);
  return (
    <form onSubmit={event => {
                                     event.preventDefault();
                                     event.target.reset();
                                     setIsBlocking(false);}} >
      <Prompt when={isBlocking}
             message={location =>
                                      `Are you sure you want to go to ${location.pathname}`} />
      <p>Blocking?{" "} {isBlocking ? "Yes, click a link or the back button" : "Nope"}</p>
      <p><input size="50" placeholder="type something to block transitions"
                   onChange={event => {setIsBlocking(event.target.value.length > 0);}} /></p>
      <p><button>Submit to stop blocking</button></p>
    </form>
  );}