Quick (untested) overview of how to lazy load Prebid.js ad units on scroll using node in-view library

in-view-ad-controller.js

import inView from 'in-view'

class InViewAdController {
  /**
   * @func didLoadDOMContent
   * @desc Hook for firing after we're sure DOM content is loaded
   */

  constructor () {
    this.setGlobals()
    this.ads = []
    this.offset = -200
    this.getAdUnits()
    this.addInViewEventListeners()
  }

  /**
   * @func setGlobals
   * @desc Ensures all globals are set safely before we use them
   */

  setGlobals () {
    window.pbjs = window.pbjs || {}
    window.pbjs.que = window.pbjs.que || []
    window.googletag = window.googletag || {}
    window.googletag.cmd = window.googletag.cmd || []
  }

  /**
   * @func getAdUnits
   * @desc Gets ad units from DOM and pushes references to ads array
   */

  getAdUnits () {
    let containers = [].slice.call(document.querySelectorAll('[data-in-view-ad]'))

    let newAds = containers.reduce((ads, container) => {
      const adId = container.getAttribute('data-in-view-ad')
      if (!adId) return ads
      const ad = this.getAdUnitConfig(adId)
      if (!ad) return ads
      ad.container = container
      return [...ads, ad]
    }, [])

    console.log(`Found ${newAds.length} in-view ads`, newAds)

    this.ads = [ ...this.ads, ...newAds]
  }

  /**
   * @func injectAdUnit
   * @desc Injects ad unit
   * @param { Object } ad
   */

  injectAdUnit (ad) {
    window.googletag.cmd.push(function () {
      ad.slot = window.googletag.defineSlot(ad.config.slot, ad.sizes, ad.id).addService(window.googletag.pubads())
    })

    window.pbjs.que.push(function () {
      window.pbjs.addAdUnits(ad.config)
    })

    ad.container.innerHTML =
    `<script type='text/javascript'>
      window.googletag.cmd.push(function() {
        window.googletag.display('${ad.id}')
      });
    </script>`

    console.log(`Injected in-view ad unit ${ad.id}`, ad)
  }

  /**
   * @func getAdUnitConfig
   * @desc Return ad unit config
   * @param { String } adId
   * @return { Object }
   */

  getAdUnitConfig (adId) {
    // Get the correct ad config from your ad unit config
    // Example ad below:
    return [{
      id: adId,
      config: {
        slot: '/61424206/90sKidsOnly_BTF_MPU2',
        mediaTypes: {
          banner: {
            sizes: [
              [300, 250]
            ]
          }
        },
        bids: [{
          // Bidder configs
        }]
      }
    }].find((ad) => ad.id === adId)
  }

  /**
   * @func addInViewEventListeners
   * @desc Adds inView event listeners for lazy loading ads
   */

  addInViewEventListeners () {
    inView.offset(this.offset)

    this.ads.forEach(ad => {
      inView(`[data-in-view-ad="${ad.id}"`).once('enter', () => {
        this.injectAdUnit(ad)
        this.requestBidsForAdUnit(ad)
        this.setTargetingForAdUnit(ad)
      })
    })
  }

  requestBidsForAdUnit (ad) {
    window.pbjs.que.push(() => {
      window.pbjs.requestBids({
        timeout: 1500,
        adUnitCodes: [ad.id]
      })
    })
  }

  /**
   * @func setTargetingForAdUnit
   * @desc Sets the targeting for the ad unit
   * @param { Object } ad
   */

  setTargetingForAdUnit (ad) {
    window.googletag.cmd.push(() => {
      window.pbjs.que.push(() => {
        window.googletag.enableServices()
        window.pbjs.setTargetingForGPTAsync([ad.id])
        window.googletag.pubads().refresh([ad.config.slot])
      })
    })
  }
}

index.html

<div data-in-view-ad="your-config-id">
  <!-- Just create an empty div and style it with the right size for the ad unit -->
</div>