Defer secondary portions of the DOM using `requestAnimationFrame`

NonBlockingRenderLoop.js

import { Component, PropTypes } from 'react'
import { noop } from 'lodash'
import raf from 'raf'

const cache = new Map()

export function createNonBlockingRenderLoop({ key, concurrencyLevel = 1 }) {
  if (cache.has(key)) {
    return cache.get(key)
  }

  let slots = 0
  const isBusy = () => slots >= concurrencyLevel
  const takeSlot = () => slots++
  const releaseSlot = () => slots--

  class NonBlockingRenderLoop extends Component {
    state = {
      wait: true
    }

    componentDidMount() {
      this.enqueue()
    }

    componentWillUnmount() {
      this.stop()
    }

    render() {
      return this.state.wait ? null : this.props.children
    }

    enqueue() {
      if (isBusy()) {
        this.defer(() => this.enqueue())
      } else {
        takeSlot()
        this.defer(() => this.dequeue())
      }
    }

    dequeue() {
      this.setState({ wait: false })
      releaseSlot()
    }

    defer(fn) {
      raf(() => {
        if (this.defer !== noop) {
          fn()
        }
      })
    }

    stop() {
      this.defer = noop
      if (this.state.wait) {
        releaseSlot()
      }
    }
  }

  NonBlockingRenderLoop.propTypes = {
    children: PropTypes.element.isRequired
  }

  cache.set(key, NonBlockingRenderLoop)
  return NonBlockingRenderLoop
}