Generate reversed range with supplied bounds

Question

This question is similar to an existing one: Create array of all integers between two numbers, inclusive, in Javascript/jQuery

However, instead of simply generating a range between two bounds min and max, I'd like to create a range between to numbers start and end with a specified limit.

Example:

start 19
end 30
limit 60

Result: [19, 20, 21, 22, ..., 28, 29, 30]

Whereas
start 30 <--\
end 19 <--/
limit 60

Result: [30, 31, 32, ..., 58, 59, 60, 1, 2, 3, ..., 17, 18, 19]

Note that: No element of the array can ever be greater than limit.

I'm guessing I'd also have to define a lower limit (1 in this case to exclude zero fro the array).

How can I achieve this in plain ES6?

what is the result for `start : 10 , end : 20 ,limit : 15` values ? — Ehsan Nazeri, Jun 09 '20 at 20:35
@EhsanNazeri That will be `[10, 11, ..., 14, 15]` - `limit` should have the highest precedence in that case (no number can ever be greater than `limit`) — j3141592653589793238, Jun 09 '20 at 20:36
So just `if (start > end) return [...range(start, limit), ...range(0, end)] else return range(start, end)`? — Bergi, Jun 09 '20 at 20:41
@Bergi Haha, I love how people can turn problems that seems difficult at first into a very simple one! Yeah, that's exactly it — j3141592653589793238, Jun 09 '20 at 20:42
@Bergi it has a problem. change it to this `if (start > end) return [...range(start, limit), ...range(0, end)] else return range(start, Math.min([end,limit])` — Ehsan Nazeri, Jun 09 '20 at 20:47
Either of you feel free to take the credit and provide an answer if you like — j3141592653589793238, Jun 09 '20 at 20:50
@EhsanNazeri I didn't think end (or start) could be larger than limit, but yeah that's a nice edge case requiring treatment :-) — Bergi, Jun 09 '20 at 20:52

score 0 · Answer 1 · answered Jun 10 '20 at 07:22

Here's my implementation of this, maybe not the best one, but it works.

It determines the direction of the range using Math.sign(end-start), and has min and max parameters:

const range = ({
  start,
  end,
  min = -Infinity,
  max = Infinity
}) => {
  if(Math.floor(start) !== start || Math.floor(end) !== end) throw new Error('Invalid numbers')
  const 
    sign = Math.sign(end - start),
    arr = [],
    push = n => {
      if (min <= n && n <= max) arr.push(n)
    }
  for (let n = start; n !== end; n += sign)
    push(n)
  push(end)
  return arr
}

console.log(range({start: 30, end: 19, max: 60}))

Generate reversed range with supplied bounds

Example:

1 Answers1