Classes VS DOM Events Handling Benchmark

benchmark-dom-classes.js

// Players
class ClickCounter {
  constructor() { this.clicks = 0; }
  onclick(e) { this.clicks += (e.type === 'click') ? 1 : -1; }
}

class Handler extends ClickCounter {
  constructor(currentTarget) {
    super();
    currentTarget.addEventListener('click', this);
  }
}

class DynamicHandler extends Handler {
  handleEvent(e) { this['on' + e.type](e); }
}

class StaticHandler extends Handler {
  handleEvent(e) { switch (e.type) {
    case 'click': return this.onclick(e);
  }}
}

// just to rule out hierarchy performance
class Bounder extends ClickCounter {
  constructor(currentTarget) { super(); }
}

class ArrowHandler extends Bounder {
  constructor(currentTarget) {
    super(currentTarget);
    this.click = (e) => this.onclick(e);
    currentTarget.addEventListener('click', this.click);
  }
}

class BoundHandler extends Bounder {
  constructor(currentTarget) {
    super(currentTarget);
    this.onclick = this.onclick.bind(this);
    currentTarget.addEventListener('click', this.onclick);
  }
}

// Rules
const benchmark = (Class, length = 1000, samples = 5) => {

  const currentTarget = button(Class.name);
  const instances = new Array(length);

  return new Promise(res => setTimeout(res, 500)).then(() => {

    let benchName;
    let memory;

    benchName = `new ${Class.name}(currentTarget)`;
    memory = performance.memory.usedJSHeapSize;
    console.time(benchName);
    for (let i = 0; i < length; i++)
      instances[i] = new Class(currentTarget);
    console.timeEnd(benchName);
    memory = performance.memory.usedJSHeapSize - memory;
    if (memory) console.log('memory: ', memory);

    const event = new Event('click');
    benchName = 'currentTarget.dispatchEvent(clickEvent)';
    memory = performance.memory.usedJSHeapSize;
    console.time(benchName);
    for (let i = 0; i < samples; i++)
      currentTarget.dispatchEvent(event);
    console.timeEnd(benchName);
    memory = performance.memory.usedJSHeapSize - memory;
    if (memory) console.log('memory: ', memory);

    console.assert(
      instances.every(instance => instance.clicks === samples),
      `expected ${length} clicks, got ${instances[0].clicks} instead`
    );

  });

};

// Helpers
const button = textContent => {
  const el = document.createElement('button');
  el.textContent = textContent;
  return document.body.appendChild(el);
};

// Race !
var instances = 10000;    // how many instances ?
var dispatches = 10;      // how many dispatches ?
Promise
  .resolve()
  .then(() => benchmark(DynamicHandler, instances, dispatches))
  .then(() => benchmark(StaticHandler, instances, dispatches))
  .then(() => benchmark(ArrowHandler, instances, dispatches))
  .then(() => benchmark(BoundHandler, instances, dispatches))
;

I guess instead of "expected ${length} clicks, got ${instances[0].clicks} instead" we should use "expected ${samples} clicks, got ${instances[0].clicks} instead", aren't we?

Just one more thing.
I launched a code of this benchmark (Chrome Version 64.0.3282.186 (Official Build) (64-bit), MacOS High Sierra) and got some different results, which shows an enormous memory consumption for handleEvent.
@WebReflection, can you, please, comment on that?

I've posted a question on StackOverflow.
The answer is pretty simple.
handleEvent consumed that much memory due to issue in the benchmark.
The thing is that strings concatenation ('on' + e.type) causes new string allocation in heap on each iteration.
If we just replace this['on' + e.type] to switch(e.type) {case 'click': this.onclick(e);}, then we get results, which are reflecting initial idea regarding benefits of using handleEvent.