rainbowloop.js

// espruino + 16 GRB Neopixels on a loop
var neopixel = require('neopixel');

var pixels = new Uint8Array(16*3);

var j = 0;
setInterval(function () {
  j = (j + 17) % 768;
  var o = 0;
  for (var i = 0; i < 16; i++) {
    var rgb = hue2rgb(i * 48 + j);
    pixels[o++]=((rgb >> 8) & 0xff) >> 3;
    pixels[o++]=((rgb >> 16) & 0xff) >> 3;
    pixels[o++]=(rgb & 0xff) >> 3;
    //pixels[o++]=(7-i);
  }
  neopixel.write(D4,pixels);
}, 66);

function hue2rgb(h) {
  h = h % 768;
  return h < 256 ? (((255 - h) << 16) | (h << 8)) :
         h < 512 ? (((511 - h) << 8) | (h - 256)) :
                    ((767 - h) | ((h - 512) << 16));
}