Create multiple timers with just one setTimeout call

create-timer.js

function createPromise () {
  let resolve, reject

  // eslint-disable-next-line promise/param-names
  const promise = new Promise((...args) => ([resolve, reject] = args))

  return { promise, resolve, reject }
}

const remove = (a, y) => (
  index => (index >= 0)
    ? [...a.slice(0, index), ...a.slice(index + 1)]
    : a
)(a.findIndex(x => (x === y)))

export const createTimer = () => (eventTarget => {
  let { promise, resolve, reject } = createPromise()
  let canceled = false

  Promise.resolve().then(async () => {
    while (!canceled) {
      promise.catch(() => (canceled = true))
      
      await new Promise(r => setTimeout(r, 1))

      resolve()

      ;({ promise, resolve, reject } = createPromise())
    }
  })

  const timers = {}
  const cbs = {}

  async function addCallback (cb, delay) {
    eventTarget.addEventListener(delay, cb)

    cbs[delay] = [...(cbs[delay] || []), cb]
    
    if (timers[delay]) return

    timers[delay] = performance.now()

    while (!canceled && timers[delay]) {
      try { await promise } catch (e) {}

      const now = performance.now()

      if ((now - timers[delay]) >= delay) {
        timers[delay] = now

        eventTarget.dispatchEvent(new Event(delay))
      }
    }
  }

  function removeCallback (cb, delay) {
    if (!cbs[delay] || !cbs[delay].includes(cb)) return
    
    eventTarget.removeEventListener(delay, cb)

    cbs[delay] = remove(cbs[delay], cb)

    if (!cbs[delay].length) {
      delete cbs[delay]
      delete timers[delay]
    }
  }

  return {
    set: addCallback, unset: removeCallback,
    destroy () {
      reject()
      delete this.set
      delete this.unset
      delete this.destroy
    }
  }
})(new EventTarget())