A little JS timing utility

stopwatch.js

class Stopwatch {
  constructor(name, silent = false) {
    this.silent = silent;
    this.samples = [];
    this.reset(name);
  }

  reset(name) {
    this.name = name;
    this.last = performance.now();
    this.samples.length = 0;
  }

  prep() {
    this.last = performance.now();
  }

  click() {
    const now = performance.now();
    const delta = now - this.last;
    if (!this.silent) {
      print(`${this.name}: ${delta.toFixed(3)}ms`);
    }
    this.samples.push(delta);
    this.last = now;
  }

  min() {
    if (this.samples.length === 0) {
      return 0;
    }
    let min = Infinity;
    for (const sample of this.samples) {
      if (sample < min) {
        min = sample;
      }
    }
    return min;
  }

  max() {
    let max = 0;
    for (const sample of this.samples) {
      if (sample > max) {
        max = sample;
      }
    }
    return max;
  }

  mean() {
    let sum = 0;
    for (const sample of this.samples) {
      sum += sample;
    }
    return sum / this.samples.length;
  }

  stddev() {
    const mean = this.mean();
    const squaredDevs = this.samples.map(x => (x - mean) ** 2);
    let devSum = 0;
    for (const squaredDev of squaredDevs) {
      devSum += squaredDev;
    }
    const variance = devSum / this.samples.length;
    const stddev = Math.sqrt(variance);
    return stddev;
  }

  median() {
    const median = this.samples[Math.floor(this.samples.length / 2)];
    return median;
  }

  printSummary() {
    print(`${this.name}:`);
    print(`  Time (mean ± σ):   ${this.mean().toFixed(3)}ms ± ${this.stddev().toFixed(3)}ms`);
    print(`  Range (min … max): ${this.min().toFixed(3)}ms … ${this.max().toFixed(3)}ms`);
  }

  printSummaryCSV(includeHeaderRow = true) {
    if (includeHeaderRow) {
      print("mean,stddev,min,max");
    }
    print(`${this.mean()},${this.stddev()},${this.min()},${this.max()}`);
  }
}