lazy-stuff.js

function drop(iterator, amount) {
  for (let i = 0; !(i >= amount); ++i) {
    if (iterator.next().done) {
      break;
    }
  }

  return iterator;
}

function* sliceLazy(iterable, start, end) {
  let counter = end - start;
  if (counter === 0) {
    return;
  }

  for (const value of drop(iterable[Symbol.iterator](), start)) {
    yield value;

    if (--counter === 0) {
      break;
    }
  }
}

function* splitLazy(string, delimiter, limit = -1) {
  switch (limit >>>= 0) {
    case 0: return;
    case 1: return void (yield string);
  }

  let i = -1;
  for (let count = 1; ;) {
    const start = i;
    if ((i = string.indexOf(delimiter, i + 1)) === -1) {
      i = start;
      break;
    }

    yield string.slice(start, i);
    i += delimiter.length;

    if (++count >= limit) {
      break;
    }
  }

  return void (yield string.slice(i));
}