WebUSB / Headphone connection to Espruino

So after a bit of fiddling, I've come up with the following that seems to work. I'm sure this has been done before and in a better and more reliable way, but this is what I have.

PC Sound Generator:

AudioContext = window.AudioContext || window.webkitAudioContext;
audioContext = new AudioContext();

gainNode = audioContext.createGain();
gainNode.gain.value = 1;

var buffer = audioContext.createBuffer(1, 44100, 44100);
var b = buffer.getChannelData(0);

function fillAt(arr, val, at, len) {
  arr.fill(val, at, at+len);
}

function charToBinary(char) {
  var bin = char.charCodeAt(0).toString(2);
  return new Array(9 - bin.length).join('0') + bin;
}

b.fill(-1.0);

function writeBinary(offset, binary) {
  if (!binary) {
    binary = '00000000';
  }
  
  var data = binary.split('');
  // Bit preamble
  fillAt(b, 1.0, offset+4, 2);
  fillAt(b, 1.0, offset+300, 2);
  // Data
  data[0] === '1' && fillAt(b, 1.0, offset+304, 2);
  data[1] === '1' && fillAt(b, 1.0, offset+308, 2);
  data[2] === '1' && fillAt(b, 1.0, offset+312, 2);
  data[3] === '1' && fillAt(b, 1.0, offset+316, 2);
  data[4] === '1' && fillAt(b, 1.0, offset+320, 2);
  data[5] === '1' && fillAt(b, 1.0, offset+324, 2);
  data[6] === '1' && fillAt(b, 1.0, offset+328, 2);
  data[7] === '1' && fillAt(b, 1.0, offset+332, 2);
  // Bit postamble
  fillAt(b, 1.0, offset+336, 2);
  fillAt(b, 1.0, offset+632, 2);
  
  return offset+632;
}

function writeString(str) {
  var chars = str.split('');
  var lastOffset = 0;
  
  for(var i = 0; i < chars.length; i++) {
    var char = chars[i];
    var bin = charToBinary(char);
    lastOffset = writeBinary(lastOffset, bin);
  }
}

// Stream start
fillAt(b, 1.0, 0, 2);

writeString('abcdefghijklmnopqrstuvwxyz'­);


source = audioContext.createBufferSource();
source.buffer = buffer;
source.connect(gainNode);
gainNode.connect(audioContext.destinatio­n);
source.start();

Espruino Receiver:

let readBits = false;
let bits = [];

function handlePulse(e) {
  const diff = e.time - e.lastTime;

  //console.log(diff);
  
  if (diff > 1.0 || isNaN(diff)) {
    if (readBits) {
      //console.log('stop reading bits');
      readBits = false;
    }
    return;
  }

  const zeroes = (diff.toFixed(4) * 10000).toFixed(1);

  if (zeroes > 50) {
    if (readBits) {
      //console.log('stop reading bits');
      readBits = false;
      bits.pop();
      
      //console.log(bits);
      var str = bits.join('');
      var num = parseInt(str, 2);
      var chr = String.fromCharCode(num);
      console.log(chr);
      bits = [];
    } else {
      //console.log('start reading bits');
      readBits = true;
    }
    
    return;
  }

  if (readBits) {
    //console.log(diff);
    //console.log(zeroes);

    for(var i = 0; i < zeroes; i++) {
      bits.push(0);
    }

    bits.push(1);
  }
}

function onInit() {
  pinMode(A5, 'input_pullup');
  setWatch(handlePulse, A5, { repeat: true, edge: 'rising' });
}

So now my question @Gordon, is how do I reverse this? i.e generate sound on Espruino. I'm guessing I want to just be doing digitalWrite to the pin I have wired to my headphone socket, can I reuse any of the code I have or should I start again?