How to make web audio / tone.js play while iphone is muted.

gistfile1.txt

// This gist copyright IdleBit 2022, MIT License

var isIOS = /iPad|iPhone|iPod/.test(navigator.platform) || (navigator.platform === 'MacIntel' && navigator.maxTouchPoints > 1)
var isMobile = /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent) || isIOS
var isFirefox = /Firefox/i.test(navigator.userAgent)

// call this from first click action
function startSound() {
  if (isIOS) {
    try{
      // Adapted from https://github.com/swevans/unmute (MIT 2020)
      const silentAudioFile = createSilentAudioFile(44100)
      createHtmlAudio(silentAudioFile);
    }catch(e){
      console.log(e)
    }
  }

  // start your web audio or tone.js sounds here.
  ...
}

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

  audio.setAttribute('x-webkit-airplay', 'deny')
  audio.preload = 'auto'
  audio.loop = true
  audio.src = silentAudioFile
  audio.load()

  audio.play().then(
    () => {
      audio.pause()
      audio.removeAttribute('src')
      audio.load()
      audio = null
    },
    () => {
      audio.pause()
      audio.removeAttribute('src')
      audio.load()
      audio = null
    }
  )
}