Write a JavaScript program to add an event listener to an element with the ability to use event delegation

const on = (el, evt, fn, opts = {}) => {
  const delegatorFn = e => e.target.matches(opts.target) && fn.call(e.target, e);
  el.addEventListener(evt, opts.target ? delegatorFn : fn, opts.options || false);
  if (opts.target) return delegatorFn;
};

const fn = () => console.log('!');
console.log(on(document.body, 'click', fn));  
console.log(on(document.body, 'click', fn, { target: 'p' }));  
console.log(on(document.body, 'click', fn, { options: true }));