Improve Neopixel Peformance?

@allObjects: Line 18 doesn't matter as it was just used to get an idea of the execution time simulating some random merging of per-calculated values. I'll use the require(), that's good.

@Gordon: I didn't get what function do you mean using ".set". I'd say setting RGB values at runtime is most likely too slow in most cases.

Having this thread resurrected, I did a quick rainbow implementation.

//rainbow effect

const pin = NodeMCU.D5;
pinMode(pin, "output");
var neopixel = require("neopixel");

//array with rgb values as Uint8ClampedArray
var rgb = [];  //length = 255/step = max. number of leds
const step = 3;  //integer n, use every n-th rainbow color, effect will be n times faster
//const leds = 64; //the number of leds, used by the slower version only

//
//getRainbowColor(position = 0..255)
//returns color of rainbow at the position as rgb in a Uint8ClampedArray
//
var getRainbowColor = function (position) {
var rgb = new Uint8ClampedArray(3);
  if(position < 85) {
   rgb[0] = position * 3;
   rgb[1] = 255 - position * 3;
   rgb[2] = 0;
  } else if (position < 170) {
   position -= 85;
   rgb[0] = 255 - position * 3;
   rgb[1] = 0;
   rgb[2] = position * 3;
  } else {
   position -= 170;
   rgb[0] = 0;
   rgb[1] = position * 3;
   rgb[2] = 255 - position * 3;
  }
  return rgb;
};

//
//prepare ()
//
//prefill the rgb array
var prepare = function() {
  for (var i=0; i<255; i += step) {
    rgb.push(getRainbowColor(i));
  }
};

//
//animate
//
var tmp;
var animate = function() {
  //rgb.push(rgb.shift());                   //rotate the rgb array by one value
  rgb.unshift(rgb.pop());                    //rotate the rgb array by one value, a little bit faster
  neopixel.write(pin, rgb);                  //faster version
  //neopixel.write(pin, rgb.slice(1, leds)); //slower version, technically cleaner
};


var onInit = function() {
  prepare();
  setInterval(function() { animate();}, 10); //10ms, if using serial/bt/wifi this might too fast
};

onInit(); //don't save() this line

If you have any suggestions on how to make the code faster please give me a hint. And if you want it to https://www.espruino.com/WS2811 feel free to copy it.