How do I correctly use setInterval and clearInterval to switch between two different functions?

Question

For practice I am trying to display a number that increments from 0 - 9, then decrements from 9 - 0, and infinitely repeats.

The code that I have so far seems to

Answer 1

    /** Tools */
const log = require('ololog').configure({
  locate: false
})

let count = 0
let interval__UP
let interval__DOWN

function countUp () {
  count++
  log.green('countUp(): ', count)

  if (count == 5) {
    clearInterval(interval__UP)
    interval__DOWN = setInterval(function () {
      countDown()
    }, 1000)
  }

}

function countDown () {

  count--
  log.red('countDown(): ', count)

  if (count == 0) {
    clearInterval(interval__DOWN)
    interval__UP = setInterval(function () {
      countUp()
    }, 3000)
  }
}

function start () {
  countUp()
  log.cyan('start()')
  interval__UP = setInterval(function () {
    countUp()
  }, 2000)
}

start()

Console Log shows it's working