speedometer test, a window sliding algorithm to calculate streaming data speed in javascript, cloud be used in any node.js stream

speedometer.js

var tick = 1;
var maxTick = 65535;
var resolution = 4;
var timer;

const startedAt = new Date().getTime();

module.exports = function(seconds) {
  var size = resolution * (seconds || 5);
  var buffer = [0];
  var pointer = 1;
  var last = (tick - 1) & maxTick;
  var inc = function() {
    tick = (tick + 1) & maxTick;

    console.log(`$ ${new Date().getTime() - startedAt}ms passed. buffer ${buffer}`);
  };

  if (!timer) {
    timer = setInterval(inc, (1000 / resolution) | 0);
    if (timer.unref) timer.unref();
  }
  console.log(`$ ${new Date().getTime() - startedAt}ms passed. buffer ${buffer}`);
  return function(delta) {
    var dist = (tick - last) & maxTick;
    if (dist > size) dist = size;
    last = tick;

    while (dist--) {
      if (pointer === size) pointer = 0;
      buffer[pointer] = buffer[pointer === 0 ? size - 1 : pointer - 1];
      pointer++;
    }

    if (delta) buffer[pointer - 1] += delta;

    var top = buffer[pointer - 1];
    var btm = buffer.length < size ? 0 : buffer[pointer === size ? 0 : pointer];
    console.log(
      `$ ${new Date().getTime() -
        startedAt}ms passed. buffer ${buffer} top ${top} top index ${pointer -
        1} btm ${btm} btm index  ${buffer.length < size ? 'null' : pointer === size ? 0 : pointer}`,
      `value  ${buffer.length < resolution ? top : ((top - btm) * resolution) / buffer.length}`,
    );
    return buffer.length < resolution ? top : ((top - btm) * resolution) / buffer.length;
  };
};

test.js

// Hi - thanks for taking the time to read this code.

// It uses a regular sliding window that is updated (per default every 1/4th second)
// Basically there is a an array that has size buffer-this-many-seconds * 4 (the default is 5s)
// and two pointers top and btm that points to the newest entry in this buffer and the oldest one.
// Every 1/4th second the top pointer is incremented and if it is bigger than the array is it reset to 0.
// When top === btm we increment btm as well (as the oldest entry is now outdated).

// When ever you update the speedometer with a delta value we increment array[top] with this value and when the top pointer is incremented we copy the value to the new top entry.

// To calculate the speed we now just need to (array[top] - array[btm]) / 5 since that gives us the delta speed in the last 5s.

const speedometer = require('./speedometer');
const speed = speedometer(2);
setTimeout(() => {
  speed(3);
  speed(3);
  setTimeout(() => {
    speed(1);
  }, 300);
  setTimeout(() => {
    speed(0);
  }, 500);
  setTimeout(() => {
    speed(2);
  }, 400);
  setTimeout(() => {
    speed(3);
    speed(3);
    setTimeout(() => {
      speed(1);
    }, 300);
    setTimeout(() => {
      speed(0);
    }, 500);
    setTimeout(() => {
      speed(2);
    }, 400);
  }, 500);
  setTimeout(() => {
    speed(0);
  }, 2100);
  setTimeout(() => {
    speed(0);
  }, 2500);
}, 2050);