stats.js

function average(values) {
  let total = 0;

  for (let i = 0; i < values.length; i += 1) {
    total += values[i];
  }

  return total / values.length;
}

function median(values) {
  const half = Math.floor(values.length / 2);

  values.sort((a, b) => a - b);

  if (values.length % 2) return values[half];

  return (values[half - 1] + values[half]) / 2;
}

function quartile(values, percentile) {
  values.sort((a, b) => a - b);
  const pos = (values.length - 1) * percentile;
  const base = Math.floor(pos);
  const rest = pos - base;

  if (values[base + 1] !== undefined) {
    return values[base] + rest * (values[base + 1] - values[base]);
  }

  return values[base];
}

function jitter(values) {
  // Average distance between consecutive latency measurements...
   let jitters = [];

  for (let i = 0; i < values.length - 1; i += 1) {
    jitters.push(Math.abs(values[i] - values[i+1]));
  }

  return average(jitters);
}

exports.average = average;
exports.median = median;
exports.quartile = quartile;
exports.jitter = jitter;