How to use the @sanity/observable/multicast function in @sanity/observable

// @flow
import Multicast from '@sanity/observable/multicast'
import Observable from '@sanity/observable'

import {uploadImageAsset} from '../inputs/client-adapters/assets'

const uploadRequests$ = new Multicast

const CONCURRENCY = 4

const registry = []
export function createUploadId(file: File): number {
  const id = registry.length
  const events = new Multicast
  registry[id] = {
    file,
    events$: events.asObservable().do({
      complete: () => {
        registry[id] = null
      }}),
    _multicast: events
  }
  return id

export function createUploadId(file: File): number {
  const id = registry.length
  const events = new Multicast
  registry[id] = {
    file,
    events$: events.asObservable().do({
      complete: () => {
        registry[id] = null
      }}),
    _multicast: events
  }
  return id
}