PeerJS photo sharing example - receiver

receiver.js

document.addEventListener('DOMContentLoaded', event => {
  const peer = new Peer('receiver', {
    host: 'localhost',
    port: 9000,
    path: '/'
  })

  peer.on('connection', conn => {
    conn.on('data', data => {
      if (data.filetype.includes('image')) {
        const bytes = new Uint8Array(data.file)
        const img = document.createElement('img')
        img.src = 'data:image/png;base64,' + encode(bytes)
        document.querySelector('div').prepend(img)
      }
    })
  })
})

const encode = input => {
  const keyStr =
    'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/='
  let output = ''
  let chr1, chr2, chr3, enc1, enc2, enc3, enc4
  let i = 0

  while (i < input.length) {
    chr1 = input[i++]
    chr2 = i < input.length ? input[i++] : Number.NaN // Not sure if the index
    chr3 = i < input.length ? input[i++] : Number.NaN // checks are needed here

    enc1 = chr1 >> 2
    enc2 = ((chr1 & 3) << 4) | (chr2 >> 4)
    enc3 = ((chr2 & 15) << 2) | (chr3 >> 6)
    enc4 = chr3 & 63

    if (isNaN(chr2)) {
      enc3 = enc4 = 64
    } else if (isNaN(chr3)) {
      enc4 = 64
    }
    output +=
      keyStr.charAt(enc1) +
      keyStr.charAt(enc2) +
      keyStr.charAt(enc3) +
      keyStr.charAt(enc4)
  }
  return output
}