Demystifying Async Programming in Javascript - Generator internals adder state machine

generator-internals-adder-state-machine.js

function adder(initialValue) {
  let state = 'initial';
  let done = false;
  let sum = initialValue;
  function go(input) {
    let result;
    switch (state) {
      case 'initial':
        result = initialValue;
        state = 'loop';
        break;
      case 'loop':
        sum += input;
        result = sum;
        state = 'loop';
        break;
      default:
        break;
    }
    return {done: done, value: result};
  }
  return {
    next: go
  }
}
function runner() {
  const add = adder(0);
  console.log(add.next()); // 0
  console.log(add.next(1)); // 1
  console.log(add.next(2)); // 3
  console.log(add.next(3)); // 6
}
runner();