Demystifying Async Programming in Javascript - Generator counts()

generator-counts.js

function* counts(start) {
  yield start + 1;
  yield start + 2;
  yield start + 3;
  return start + 4;
}
const counter = counts(0);
console.log(counter.next()); // {value: 1, done: false}
console.log(counter.next()); // {value: 2, done: false}
console.log(counter.next()); // {value: 3, done: false}
console.log(counter.next()); // {value: 4, done: true}
console.log(counter.next()); // {value: undefined, done: true}