Demystifying Async Programming in Javascript - Generator internals printer state machine

generator-internals-printer-state-machine.js

function printer(start) {
  let state = 0;
  let done = false;
  function go(input) {
    let result;
    switch (state) {
      case 0:
        console.log("We are starting!");
        state = 1;
        break;
      case 1:
        console.log(input);
        state = 2;
        break;
      case 2:
        console.log(input);
        state = 3;
        break;
      case 3:
        console.log(input);
        console.log("We are done!");
        done = true;
        state = -1;
        break;
      default:
        break;
      return {done: done, value: result};
    }
  }
  return {
    next: go
  }
}
const counter = printer();
counter.next(1); // We are starting!
counter.next(2); // 2
counter.next(3); // 3
counter.next(4); // 4
counter.next(5); // We are done!