index.js

/*! unmute-ios-audio. MIT License. Feross Aboukhadijeh <https://feross.org/opensource> */
module.exports = unmuteIosAudio

const USER_ACTIVATION_EVENTS = [
  'auxclick',
  'click',
  'contextmenu',
  'dblclick',
  'keydown',
  'keyup',
  'mousedown',
  'mouseup',
  'touchend'
]

function unmuteIosAudio () {
  const AudioContext = window.webkitAudioContext

  // To detect iOS, check for touch device and confirm Safari-only
  // webkitAudioContext is present.
  const isIos = navigator.maxTouchPoints > 0 && AudioContext != null

  if (!isIos) return

  // state can be 'blocked', 'pending', 'allowed'
  let htmlAudioState = 'blocked'
  let webAudioState = 'blocked'

  let audio
  let context
  let source

  const sampleRate = (new AudioContext()).sampleRate
  const silentAudioFile = createSilentAudioFile(sampleRate)

  USER_ACTIVATION_EVENTS.forEach(eventName => {
    window.addEventListener(
      eventName, handleUserActivation, { capture: true, passive: true }
    )
  })

  // Return a seven samples long 8 bit mono WAVE file
  function createSilentAudioFile (sampleRate) {
    const arrayBuffer = new ArrayBuffer(10)
    const dataView = new DataView(arrayBuffer)

    dataView.setUint32(0, sampleRate, true)
    dataView.setUint32(4, sampleRate, true)
    dataView.setUint16(8, 1, true)

    const missingCharacters =
      window.btoa(String.fromCharCode(...new Uint8Array(arrayBuffer)))
        .slice(0, 13)

    return `data:audio/wav;base64,UklGRisAAABXQVZFZm10IBAAAAABAAEA${missingCharacters}AgAZGF0YQcAAACAgICAgICAAAA=`
  }

  function handleUserActivation (e) {
    if (htmlAudioState === 'blocked') {
      htmlAudioState = 'pending'
      createHtmlAudio()
    }
    if (webAudioState === 'blocked') {
      webAudioState = 'pending'
      createWebAudio()
    }
  }

  function createHtmlAudio () {
    audio = document.createElement('audio')

    audio.setAttribute('x-webkit-airplay', 'deny') // Disable the iOS control center media widget
    audio.preload = 'auto'
    audio.loop = true
    audio.src = silentAudioFile
    audio.load()

    audio.play().then(
      () => {
        htmlAudioState = 'allowed'
        maybeCleanup()
      },
      () => {
        htmlAudioState = 'blocked'

        audio.pause()
        audio.removeAttribute('src')
        audio.load()
        audio = null
      }
    )
  }

  function createWebAudio () {
    context = new AudioContext()

    source = context.createBufferSource()
    source.buffer = context.createBuffer(1, 1, 22050) // .045 msec of silence
    source.connect(context.destination)
    source.start()

    if (context.state === 'running') {
      webAudioState = 'allowed'
      maybeCleanup()
    } else {
      webAudioState = 'blocked'

      source.disconnect(context.destination)
      source = null

      context.close()
      context = null
    }
  }

  function maybeCleanup () {
    if (htmlAudioState !== 'allowed' || webAudioState !== 'allowed') return

    USER_ACTIVATION_EVENTS.forEach(eventName => {
      window.removeEventListener(
        eventName, handleUserActivation, { capture: true, passive: true }
      )
    })
  }
}