pager.ts

const fake = () => {
  let _data = [];
  for (i = 0, l = 46; i < l; i++) {
    let card = faker.helpers.userCard();      
    card.id = (i + 1);
    _data.push(card);
  }
  return _data;
}

const pager = (offset = 0, limit = 100) => {
  return Rx.Observable.range(getOffset(offset), getLimit(offset, limit));
}
                             
const getOffset = (offset) => {
   return offset > 0 ? offset : 0;
}

const getLimit = (offset, limit) => {
  const sum = (Number(offset) + Number(limit));
  return sum < data.length ? limit : data.length - offset;
}

const getNext = (offset, limit) => {
  let next = false;
  if ((offset + limit) < data.length) {
    next = {
      limit: limit,
      offset: getOffset(offset) + limit
    }

  } else if ((offset + limit) > data.length && offset < data.length) {
    next = {
      limit: getLimit(offset, limit),
      offset: data.length - getLimit(offset, limit)
    }

  }
  return next;
}

const getPrev = (offset, limit) => {
  let prev = false;
  if ((offset - limit) > 0) {
    prev = {
      limit: limit,
      offset: getOffset(offset) - limit
    }

  } else if ((offset - limit) < 0 && offset > 0) {
    prev = {
      limit: limit,
      offset: 0
    }

  }
  return prev;
}

const getLast = (offset, limit) => {
  const rest = (data.length - offset) > limit;
  if (rest) {
    return getLast(offset + limit, limit);
  }
  if (offset + limit === data.length) {
    return {
      limit: limit,
      offset: offset
    };
  }
  return getNext(offset, limit);
}

const data = fake();
let limit = 3;
let offset = 30;
const view = [];

pager(offset, limit)
  .filter((x) => {
    return data[x - 1] !== undefined;
  })
  .subscribe(
    (x) => {
      view.push(data[x - 1]);
    },
    (e) => console.error(e),
    () => {
      console.log(view);
      let _page = {
        total: data.length,
        items: view,
        limit: limit,
        offset: offset
      };
      _page.last = getLast(offset, limit);
      _page.next = getNext(offset, limit);
      _page.prev = getPrev(offset, limit);
      _page.totalPages = Math.ceil(data.length / limit);
      _page.page = Math.ceil(offset/limit);
       console.log(_page);
    }
  );