Demystifying Async Programming in Javascript - Generator internals reverting adder

generator-internals-reverting-adder.js

function* adder(initialValue) {
  let sum = initialValue;
  let lastSum = initialValue;
  let temp;
  while (true) {
    try {
      temp = sum;
      sum += yield sum;
      lastSum = temp;
    } catch (e) {
      sum = lastSum;
    }
  }
}
const add = adder(0);
console.log(add.next()); // 0
console.log(add.next(1)); // 1
console.log(add.next(2)); // 3
console.log(add.throw(new Error('BOO)!'))); // 1
console.log(add.next(4)); // 5