promisu/src/lib/PromisuThrottle/index.js

functional promise with map filter reduce scan all race every some few try waitfor finally queue debounce throttle

class AbortError extends Error {
  constructor() {
    super('Throttled function aborted')
    this.name = 'AbortError'
  }
}

const PromisuThrottle = (fn, limit, interval) => {
  if (!Number.isFinite(limit)) {
    throw new TypeError('Expected limit to be a finite number')
  }

  if (!Number.isFinite(interval)) {
    throw new TypeError('Expected interval to be a finite number')
  }

  const queue = []
  const timeouts = new Set()
  let activeCount = 0

  const next = () => {
    activeCount++

    const id = setTimeout(() => {
      activeCount--

      if (queue.length > 0) {
        next()
      }

      timeouts.delete(id)
    }, interval)

    timeouts.add(id)

    const x = queue.shift()
    x.resolve(fn.apply(x.self, x.args))
  }

  const throttled = function () {
    const args = arguments

    return new Promise((resolve, reject) => {
      queue.push({
        resolve,
        reject,
        args,
        self: this
      })

      if (activeCount < limit) {
        next()
      }
    })
  }

  throttled.abort = () => {
    for (const id of timeouts) {
      clearTimeout(id)
    }
    timeouts.clear()

    for (const x of queue) {
      x.reject(new AbortError())
    }
    queue.length = 0
  }

  return throttled
}

module.exports = PromisuThrottle