neopixel-wifi-control/main.js.h

const char main_js[] = R"=====(
window.addEventListener('load', setup);
window.addEventListener('resize', drawColorbar);

function handle_M_B_S(e) {
  e.preventDefault();
  var name = e.target.className;
  var val = e.target.id;
  if(e.target.className.indexOf('m') > -1) {
    elems = document.querySelectorAll('#mode li a');
    [].forEach.call(elems, function(el) {
      el.classList.remove('active');
      name = e.target.className;
    });
    e.target.classList.add('active');
  }
  submitVal(name, val);
}

function submitVal(name, val) {
  var xhttp = new XMLHttpRequest();
  xhttp.open('GET', 'set?' + name + '=' + val, true);
  xhttp.send();
}

function compToHex(c) {
  hex = c.toString(16);
  return hex.length == 1 ? '0' + hex : hex;
}

function getMousePos(can, evt) {
  r = can.getBoundingClientRect();
  return {
    x: evt.clientX - r.left,
    y: evt.clientY - r.top
  };
}

function Touch(e) {
  e.preventDefault();
  pos = {
    x: Math.round(e.targetTouches[0].pageX),
    y: Math.round(e.targetTouches[0].pageY)
  };
  rgb = ctx.getImageData(pos.x, pos.y, 1, 1).data;
  drawColorbar(rgb);
  submitVal('c', compToHex(rgb[0]) + compToHex(rgb[1]) + compToHex(rgb[2]));
}

function Click(e) {
  pos = getMousePos(can, e);
  rgb = ctx.getImageData(pos.x, pos.y, 1, 1).data;
  drawColorbar(rgb);
  submitVal('c', compToHex(rgb[0]) + compToHex(rgb[1]) + compToHex(rgb[2]));
}

// Thanks to the backup at http://axonflux.com/handy-rgb-to-hsl-and-rgb-to-hsv-color-model-c
function rgbToHsl(r, g, b){
  r = r / 255;
  g = g / 255;
  b = b / 255;
  var max = Math.max(r, g, b);
  var min = Math.min(r, g, b);
  var h, s, l = (max + min) / 2;
  if(max == min) {
    h = s = 0;
  } else {
    var d = max - min;
    s = l > 0.5 ? d / (2 - max - min) : d / (max + min);
    switch(max) {
      case r: h = (g - b) / d + (g < b ? 6 : 0); break;
      case g: h = (b - r) / d + 2; break;
      case b: h = (r - g) / d + 4; break;
    }
    h = h / 6;
  }
  return [h, s, l];
}

function drawColorbar(rgb = [0, 0, 0]) {
  can = document.getElementById('colorbar');
  ctx = can.getContext('2d');
  can.width = document.body.clientWidth * 0.25;
  var h = can.height / 360;
  
  var hsl = rgbToHsl(rgb[0], rgb[1], rgb[2]);
  
  for(var i=0; i<=360; i++) {
    ctx.fillStyle = 'hsl('+i+', 100%, 50%)';
    ctx.fillRect(0, i * h, can.width/2, h);
    ctx.fillStyle = 'hsl(' + hsl[0] * 360 + ', 100%, ' + i * (100/360) + '%)';
    ctx.fillRect(can.width/2, i * h, can.width/2, h);
  }
}

function setup(){
  var xhttp = new XMLHttpRequest();
  xhttp.onreadystatechange = function() {
    if (xhttp.readyState == 4 && xhttp.status == 200) {
      document.getElementById('mode').innerHTML = xhttp.responseText;
      elems = document.querySelectorAll('ul li a'); // adds listener also to existing s and b buttons
      [].forEach.call(elems, function(el) {
        el.addEventListener('touchstart', handle_M_B_S, false);
        el.addEventListener('click', handle_M_B_S, false);
      });
    }
  };
  xhttp.open('GET', 'modes', true);
  xhttp.send();
 
  var can = document.getElementById('colorbar');
  var ctx = can.getContext('2d');

  drawColorbar();
  
  can.addEventListener('touchstart', Touch, false);
  can.addEventListener('click', Click, false);
}
)=====";