Need generating a list from an object

Question

I'm working in a front-end in which I receive an order from the database and I need to generate a PDF but only wit 10 items per page. I need to generate a list of orders with the same attributes but with 10 items each until the original order items list finishes.

Here an example:

const order = {
    name: 'services',
    items: ['a', 'b', 'c', 'd', 'e', 'f', 'g'],
}

const paginate = (order, pages, start, end) => {

    if (order.items.length <= end) {
        return pages.concat({
            name: order.name,
            items: order.items.slice(start, end)
        })
    } else {
        start += 4
        end += 4
        paginate(order, start, end)
    }

}

but that gives me the Maximum call stack size exceeded error. For this example I'm trying to split the order with 3 items. Any help will be really good.

Answer 1

You will need to address some problems in your code like:

1. You've to update the pages parameter in your recursive call which you're not doing.
2. Also, I'm not sure why you have a hard-coded value of 4 for the increment of start and end, although you mentioned you want to split the order with 3 items.

My approach:

1. As a base(terminating) case, check if the start <= length of items.
   1.1. If yes, return the pages array.
2. Calculate the end for the current call.
3. Update the pages array.
4. Make the recursive call with the updated end and pages array.

const order = {
  name: 'services',
  items: ['a', 'b', 'c', 'd', 'e', 'f', 'g'],
}
// Time complexity: O(n), n being #of items in the order.items array.
const paginate = (order, itemsPerPage, start = 0, pages = []) => {
  // base case
  if (start >= order.items.length) {
    return pages; // Space Complexity O(n) for pages + depth of call stack used ~ O(n)
  }
  const end = start + itemsPerPage;
  pages.push({
    name: order.name,
    items: order.items.slice(start, end)
  });
  return paginate(order, itemsPerPage, end, pages);
}
const paginatedOrders = paginate(order, 3); // <-- update to 4 if you need that
console.log(paginatedOrders);

SIDENOTE:

As you can see it is tail recursive code(and although compilers optimize them behind the scenes), writing iterative approach for it is easier. The asymptotic time and space complexity remains O(n) although you can save the stack space when you use the iterative approach which in recursive code approximates to (n / itemsPerPage).