.js

function on(eventTarget, eventType, handler) {
  // Distinct but identical event handler
  const handler2 = (event) => handler(event);
  
  eventTarget.addEventListener(eventType, hander2);
  
  const unsub = () => {
    eventTarget.removeEventListener(eventType, hander2);
  };
  return unsub;
}

const removeClick = on(el, 'click', (event) => {});

removeClick() // removes the handler