for writing data to a compact custom binary format. serialize / save / send data over the network using the minimal amount of bits.

bitpacker.js

function bitpacker(bytes=[]) {
  return {
    bytes: bytes,
    bitcursor: 0,

    write(bitcount, value) {
           if(typeof value === 'string') value = value.charCodeAt(0)
      else if(typeof value === 'boolean') value = value?1:0
      else if(value > 2**bitcount-1) value = 2**bitcount-1 // overflow will stay at max value instead of wrapping

      for(let i=0;i<bitcount;i++) {
        const bytesi = Math.floor(this.bitcursor/8)
        if(this.bytes[bytesi] === undefined) this.bytes[bytesi] = 0
        this.bytes[bytesi] |= ((value>>>i)&1) << (this.bitcursor%8)
        //this.bytes[bytesi] |= (value&(1<<i)?1:0) << this.bitcursor%8
        this.bitcursor++
      }
    },

    read(bitcount, loopcount=1) {
      const values = new Array(loopcount)
      for(let l=0;l<loopcount;l++) {
        let value = 0
        for(let i=0;i<bitcount;i++) {
          const bytesi = Math.floor(this.bitcursor/8)
          //value |= (this.bytes[bytesi]>>>(this.bitcursor%8) & 1) << i
          value |= (this.bytes[bytesi]&(1<<(this.bitcursor%8))?1:0) << i
          this.bitcursor++
        }
        values[l] = value
      }
      return loopcount===1 ? values[0] : values
    },
  }
}







;(() => {
  // my data
  const events = [{char:'h', ms:0, err:false}, {char:'i', ms:100, err:false}]
  console.log('events', events)

  // standard JSON.stringify
  console.log('json', JSON.stringify(events)) // 67 bytes

  function serialize(events) {
    const bits = bitpacker()
    events.forEach(e => bits.write(8,  e.char))
    events.forEach(e => bits.write(13, e.ms))
    events.forEach(e => bits.write(1,  e.err))
    return bits.bytes
  }
  console.log('bitpacker', serialize(events)) // 6 bytes



  function deserialize(bytes) {
    const bits = bitpacker(bytes)
    const events    = new Array(Math.floor(bytes.length*8 / (8+13+1)))
    const chararr   = bits.read(8,  events.length)
    const msarr     = bits.read(13, events.length)
    const errarr    = bits.read(1,  events.length)
    for(let i=0;i<events.length;i++) events[i] = {char:String.fromCharCode(chararr[i]), ms:msarr[i], err:!!errarr[i]}
    return events
  }
  console.log('serialize | deserialize', deserialize(serialize(events)))


  ms = Date.now()
  for(let i=0;i<1000000;i++) JSON.stringify(events)
  console.log('json stringify took', Date.now() - ms, 'ms')
  serial = JSON.stringify(events)
  ms = Date.now()
  for(let i=0;i<1000000;i++) JSON.parse(serial)
  console.log('json parse took', Date.now() - ms, 'ms')

  ms = Date.now()
  for(let i=0;i<1000000;i++) serialize(events)
  console.log('bitpacker serialize took', Date.now() - ms, 'ms')
  serial = serialize(events)
  ms = Date.now()
  for(let i=0;i<1000000;i++) deserialize(serial)
  console.log('bitpacker deserialize took', Date.now() - ms, 'ms')
})()

// copy paste into the browser console for a demo