Iterator-generator.js

function* genRange(start, stop) {
  let curr = 0;

  while (curr < stop) yield curr++;
}

const gen = genRange(0, 3);
console.log("generator:");

for (let i of gen) {
  console.log(i); // => 0, then 1, then 2
}
for (let i of gen) {
  console.log(i); // => ...nothing
}

const iterRange = (start, stop) => {
  let current = start;
  const next = () => {
    if (current < stop) {
      return { value: current++ };
    } else {
      current = start;
      return { done: true };
    }
  };
  return { [Symbol.iterator]: () => ({ next }) };
};

const iter = iterRange(0, 3);
console.log("iterator");

for (let i of iter) {
  console.log(i); // => 0, then 1, then 2
}
for (let i of iter) {
  console.log(i); // => 0, then 1, then 2
}

const hybridRange = (start, stop) => {
  const next = function*() {
    let current = start;
    while (current < stop) {
      yield current++;
    }
  };
  return { [Symbol.iterator]: next };
};

const hybrid = hybridRange(0, 3);
console.log("hybrid");

for (let i of hybrid) {
  console.log(i); // => 0, then 1, then 2
}
for (let i of hybrid) {
  console.log(i); // => 0, then 1, then 2
}