pairWise.js

const sizedArray = (n) => Array(n).fill();

const times = (n, cb) => {
  while (0 < n--) {
    cb();
  }
}

const fillWithCb = (n, cb) => sizedArray(n).map(cb);

const nWise = n => array => {
  iterators = fillWithCb(n, () => array[Symbol.iterator]());
  iterators.forEach((it, index) => times(index, () => it.next()));
  return fillWithCb(
    array.length - n + 1,
    () => iterators.map(it => it.next().value),
  );
};

const pairWise = nWise(2);