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// cancellable async function loop

const asyncFunction = () => new Promise(resolve => {
  console.log('loop');
  setTimeout(resolve, 1000);
});


// 1

const asyncLoop1 = () => {
  let loop = true;
  const handler = () => {
    loop && asyncFunction().then(handler);
  };
  handler();
  return () => loop = false;
};

const cancel1 = asyncLoop1(); // start
cancel1(); // cancel


// 2

const asyncLoop2 = (flag = {loop: true}) => {
  asyncFunction().then(() => flag.loop && asyncLoop2(flag));
  return () => flag.loop = false;
};

const cancel2 = asyncLoop2(); // start
cancel2(); // cancel


// 3

async function asyncLoop3(signal) {
  let loop = true;
  signal.then(() => loop = false);
  while(loop) {
    await asyncFunction();
  }
}

let cancel3;
const signal = new Promise(resolve => cancel3 = resolve);
asyncLoop3(signal); // start
cancel3(); // cancel


// 4

const asyncLoop4 = () => {
  let loop = true;
  const iterator = generator();
  iterator.next();
  function* generator() {
    while(loop) {
      asyncFunction().then(() => iterator.next());
      yield;
    }
  }
  return () => loop = false;
};

const cancel4 = asyncLoop4(); // start
cancel4(); // cancel