Generators and Iterators in JavaScript #javascript #typescript

range.ts

function* range(start: number, stop?: number, step = 1): Generator<number> {
  if (stop == null) {
    stop = start;
    start = 0;
  }
  for (let i = start; step > 0 ? i < stop : i > stop; i += step) {
    yield i;
  }
}

console.log([...range(0, 10)]);

take.ts

function *take<T>(g: Iterator<T>, l: number): Generator<T> {
  for (let i = 0; i < l; i++) {
    const item = g.next();
    if (item.done) return;
    yield item.value;
  }
}

console.log([...take(range(0, 10), 3)]);

/**
 * Take n items from asynchronous iterator
 */
async function *takeAsync<T>(g: AsyncIterator<T>, l: number): AsyncGenerator<T> {
  for (let i = 0; i < l; i++) {
    const item = await g.next();
    if (item.done) return;
    yield item.value;
  }
}