const countdown = {

  [Symbol.iterator]() {

    const iterator = {

      value: 10,

      done: false,

      next() {

        this.done = this.done || this.value < 0;

​

        if (this.done) {

          return { done: true };

        } else {

          return { done: false, value: this.value-- };

        }

      },

      return(value) {

        console.log('Return to Forever')

        this.done = true;

        if (arguments.length === 1) {

          return { done: true, value };

        } else {

          return { done: true };

        }

      }

    };

​

    return iterator;

  }

};

​

function * zipWith (zipper, ...iterables) {

  const iterators = iterables.map(i => i[Symbol.iterator]());

​

  while (true) {

    const pairs = iterators.map(j => j.next()),

          dones = pairs.map(p => p.done),

          values = pairs.map(p => p.value);

​

    if (dones.indexOf(true) >= 0) {

      for (const iterator of iterators) {

        if (typeof iterator.return === 'function') {

          iterator.return();

        }

      }

      return;

    }

​

    yield zipper(...values);

  }

}

​

const fewWords = ['alper', 'bethe', 'gamow'];

​

for (const pair of zipWith((l, r) => [l, r], countdown, fewWords)) {

  //... diddley

}