ctx-dom-event-handler.js

// https://medium.com/@WebReflection/dom-handleevent-a-cross-platform-standard-since-year-2000-5bf17287fd38
export default class DOMEventHandler {
  constructor(ctx, node) {
    if (!ctx) throw new Error("DOMEventHandler: A context is required.");
    this.ctx = ctx;
    if (node) this.addEventListeners(node);
  }

  get events() {
    return (
      this._events ||
      Object.defineProperty(this, "_events", {
        value: Object.getOwnPropertyNames(this.ctx.constructor.prototype)
          .filter(type => /^on/.test(type))
          .map(type => type.slice(2))
      })._events
    );
  }

  handleEvent(event) {
    this.ctx["on" + event.type](event);
  }

  addEventListeners(node) {
    for (
      let events = this.events, i = events.length;
      i--;
      node.addEventListener(events[i], this)
    );
  }

  removeEventListeners(node) {
    for (
      let events = this.events, i = events.length;
      i--;
      node.removeEventListener(events[i], this)
    );
  }
}

my-ws-controller.js

// Example use of CTX event handler
import DOMEventHandler from "ctx-dom-event-handler"

class MyWSController extends SomeOtherClass {
  constructor () {
    this.ws = new WebSocket('ws://localhost:8080');
    this.handler = new DOMEventHandler(this, this.ws)
  }
  
  onmessage (ev) {}
  onopen (ev) {}
  onerror (ev) {}
  onclose (ev) {}
}

This turned out to be a useful pattern. I made it a module https://github.com/bcomnes/dom-event-handler