Demystifying Async Programming in Javascript - Generator printer()

generator-printer.js

function* printer() {
  console.log("We are starting!");
  console.log(yield);
  console.log(yield);
  console.log(yield);
  console.log("We are done!");
}
const counter = printer();
counter.next(1); // We are starting!
counter.next(2); // 2
counter.next(3); // 3
counter.next(4); // 4\n We are done!
counter.next(5); // <doesn't print anything>