function* fibonacci() {
  let a = 0, b = 1;
  yield a;
  yield b;
  while (true) {
    let next = a + b;
    yield next;
    a = b;
    b = next;
  }
}

const gen = fibonacci();
const results = [];
for (let i = 0; i < 6; i++) {
  results.push(gen.next().value);
}
console.log(results.join(','));